allmydata.test.cli.test_run.RunTests.test_pidfile_contents fails sometimes

[exarkun]

  File "/tmp/tahoe-lafs.tox/py39/lib/python3.9/site-packages/allmydata/test/cli/test_run.py", line 279, in test_pidfile_contents
    with check_pid_process(pidfile):
AttributeError: __enter__
Falsifying example: test_pidfile_contents(
    self=<allmydata.test.cli.test_run.RunTests.test_pidfile_contents id=0x7ff02560ca30>,
    content='0 0',
)

The regex filtering out "good" content misses some strings the parser will accept.