Use the right Python version when testing on GitHub Actions

[sajith]

We're running tox -e py27-coverage on GitHub Actions, even when we mean to run tests with Python 3.6, and so we're accidentally running them with Python 2.7.

This is the log from (macos-latest, Python 3.6):

Run tox -e py27-coverage
  tox -e py27-coverage
  shell: /bin/bash -e {0}
  env:
    TAHOE_LAFS_HYPOTHESIS_PROFILE: ci
    pythonLocation: /Users/runner/hostedtoolcache/Python/3.6.13/x64
GLOB sdist-make: /Users/runner/work/tahoe-lafs/tahoe-lafs/setup.py
py27-coverage create: /Users/runner/work/tahoe-lafs/tahoe-lafs/.tox/py27-coverage
py27-coverage installdeps: pip==19.1.1, setuptools==41.0.1, wheel==0.33.4, subunitreporter==19.3.2, certifi
ERROR: invocation failed (exit code 1), logfile: /Users/runner/work/tahoe-lafs/tahoe-lafs/.tox/py27-coverage/log/py27-coverage-1.log
================================== log start ===================================
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.

This is the log from (ubuntu-latest, Python 3.6):

Run tox -e py27-coverage
GLOB sdist-make: /home/runner/work/tahoe-lafs/tahoe-lafs/setup.py
py27-coverage create: /home/runner/work/tahoe-lafs/tahoe-lafs/.tox/py27-coverage
py27-coverage installdeps: pip==19.1.1, setuptools==41.0.1, wheel==0.33.4, subunitreporter==19.3.2, certifi
py27-coverage inst: /home/runner/work/tahoe-lafs/tahoe-lafs/.tox/.tmp/package/1/tahoe-lafs-1.14.0.post3238.zip
py27-coverage installed: /home/runner/work/tahoe-lafs/tahoe-lafs/.tox/py27-coverage/lib/python2.7/site-packages/OpenSSL/crypto.py:14: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.,  from cryptography import utils, x509,DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.,appdirs==1.4.4,atomicwrites==1.4.0,attrs==19.3.0,autobahn==19.11.2,Automat==20.2.0,backports.functools-lru-cache==1.6.4,bcrypt==3.1.7,beautifulsoup4==4.9.3,boltons==20.2.1,certifi==2020.12.5,cffi==1.14.5,chardet==4.0.0,click==7.1.2,click-default-group==1.2.2,configparser==4.0.2,constantly==15.1.0,contextlib2==0.6.0.post1,coverage==5.5,cryptography==3.3.2,decorator==4.4.2,distlib==0.3.1,distro==1.5.0,eliot==1.7.0,enum34==1.1.10,extras==1.0.0,filelock==3.0.12,fixtures==3.0.0,flake8==3.9.0,foolscap==0.13.1,funcsigs==1.0.2,functools32==3.2.3.post2,future==0.18.2,futures==3.3.0,greenlet==1.0.0,hkdf==0.0.3,html5lib==1.1,humanize==1.0.0,hyperlink==21.0.0,hypothesis==4.57.1,idna==2.10,importlib-metadata==2.1.1,importlib-resources==3.3.1,incremental==21.3.0,ipaddress==1.0.23,Jinja2==2.11.3,junitxml==0.7,linecache2==1.0.0,magic-wormhole==0.12.0,MarkupSafe==1.1.1,mccabe==0.6.1,mock==3.0.5,monotonic==1.6,more-itertools==5.0.0,netifaces==0.10.9,packaging==20.9,paramiko==2.7.2,Parsley==1.3,pathlib2==2.3.5,pbr==5.5.1,pluggy==0.13.1,py==1.10.0,pyasn1==0.4.8,pyasn1-modules==0.2.8,pycodestyle==2.7.0,pycparser==2.20,pyflakes==2.2.0,PyHamcrest==1.10.1,PyNaCl==1.4.0,pyOpenSSL==20.0.1,pyparsing==2.4.7,pyrsistent==0.16.1,pytest==4.6.11,pytest-timeout==1.4.2,pytest-twisted==1.13.2,python-mimeparse==1.6.0,python-subunit==1.4.0,pyutil==3.3.0,PyYAML==5.4.1,requests==2.25.1,scandir==1.10.0,service-identity==18.1.0,singledispatch==3.6.1,six==1.15.0,sortedcontainers==2.3.0,soupsieve==1.9.6,spake2==0.8,subunitreporter==19.3.2,tahoe-lafs==1.14.0.post3238,tenacity==7.0.0,testtools==2.4.0,toml==0.10.2,towncrier==21.3.0,tox==3.23.0,tqdm==4.60.0,traceback2==1.4.0,treq==21.1.0,Twisted==20.3.0,txaio==18.8.1,txi2p==0.3.2,txtorcon==20.0.0,typing==3.7.4.3,unittest2==1.1.0,urllib3==1.26.4,virtualenv==20.4.3,wcwidth==0.2.5,webencodings==0.5.1,zfec==1.5.5,zipp==1.2.0,zope.interface==5.3.0
py27-coverage run-test-pre: PYTHONHASHSEED='231559931'
py27-coverage run-test: commands[0] | pip freeze
/home/runner/work/tahoe-lafs/tahoe-lafs/.tox/py27-coverage/lib/python2.7/site-packages/OpenSSL/crypto.py:14: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.
  from cryptography import utils, x509
DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.

This is the log from (windows-latest, Python 3.6):

Run tox -e py27-coverage
  tox -e py27-coverage
  shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
  env:
    TAHOE_LAFS_HYPOTHESIS_PROFILE: ci
    pythonLocation: C:\hostedtoolcache\windows\Python\3.6.8\x64
GLOB sdist-make: D:\a\tahoe-lafs\tahoe-lafs\setup.py
py27-coverage create: D:\a\tahoe-lafs\tahoe-lafs\.tox\py27-coverage
py27-coverage installdeps: pip==19.1.1, setuptools==41.0.1, wheel==0.33.4, subunitreporter==19.3.2, certifi
py27-coverage inst: D:\a\tahoe-lafs\tahoe-lafs\.tox\.tmp\package\1\tahoe-lafs-1.14.0.post3238.zip
py27-coverage installed: DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.,appdirs==1.4.4,atomicwrites==1.4.0,attrs==19.3.0,autobahn==19.11.2,Automat==20.2.0,backports.functools-lru-cache==1.6.4,bcrypt==3.1.7,beautifulsoup4==4.9.3,boltons==20.2.1,certifi==2020.12.5,cffi==1.14.5,chardet==4.0.0,click==7.1.2,click-default-group==1.2.2,colorama==0.4.4,configparser==4.0.2,constantly==15.1.0,contextlib2==0.6.0.post1,coverage==5.5,cryptography==3.3.2,decorator==4.4.2,distlib==0.3.1,distro==1.5.0,eliot==1.7.0,enum34==1.1.10,extras==1.0.0,filelock==3.0.12,fixtures==3.0.0,flake8==3.9.0,foolscap==0.13.1,funcsigs==1.0.2,functools32==3.2.3.post2,future==0.18.2,futures==3.3.0,greenlet==1.0.0,hkdf==0.0.3,html5lib==1.1,humanize==1.0.0,hyperlink==21.0.0,hypothesis==4.57.1,idna==2.10,importlib-metadata==2.1.1,importlib-resources==3.3.1,incremental==21.3.0,ipaddress==1.0.23,Jinja2==2.11.3,junitxml==0.7,linecache2==1.0.0,magic-wormhole==0.12.0,MarkupSafe==1.1.1,mccabe==0.6.1,mock==3.0.5,monotonic==1.6,more-itertools==5.0.0,netifaces==0.10.9,packaging==20.9,paramiko==2.7.2,Parsley==1.3,pathlib2==2.3.5,pbr==5.5.1,pluggy==0.13.1,py==1.10.0,pyasn1==0.4.8,pyasn1-modules==0.2.8,pycodestyle==2.7.0,pycparser==2.20,pyflakes==2.2.0,PyHamcrest==1.10.1,PyNaCl==1.4.0,pyOpenSSL==20.0.1,pyparsing==2.4.7,pyrsistent==0.16.1,pytest==4.6.11,pytest-timeout==1.4.2,pytest-twisted==1.13.2,python-mimeparse==1.6.0,python-subunit==1.4.0,pyutil==3.3.0,pywin32==228,PyYAML==5.4.1,requests==2.25.1,scandir==1.10.0,service-identity==18.1.0,singledispatch==3.6.1,six==1.15.0,sortedcontainers==2.3.0,soupsieve==1.9.6,spake2==0.8,subunitreporter==19.3.2,tahoe-lafs==1.14.0.post3238,tenacity==7.0.0,testtools==2.4.0,toml==0.10.2,towncrier==21.3.0,tox==3.23.0,tqdm==4.60.0,traceback2==1.4.0,treq==21.1.0,Twisted==20.3.0,txaio==18.8.1,txi2p==0.3.2,txtorcon==20.0.0,typing==3.7.4.3,unittest2==1.1.0,urllib3==1.26.4,virtualenv==20.4.3,wcwidth==0.2.5,webencodings==0.5.1,zfec==1.5.5,zipp==1.2.0,zope.interface==5.3.0
py27-coverage run-test-pre: PYTHONHASHSEED='590'
py27-coverage run-test: commands[0] | pip freeze
DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.

[exarkun]

This was fixed along with ticket:3683 in 7c0f3d0cbf30fa9b9920db352435092dd173343d