CircleCI: Tor project's Debian package repository keys have expired

[sajith]

Here's a couple of CircleCI failures:

• ​https://app.circleci.com/pipelines/github/tahoe-lafs/tahoe-lafs/1447/workflows/05cb929d-6bcb-4900-8f4f-7b39a9c18998/jobs/37917
• ​https://app.circleci.com/pipelines/github/tahoe-lafs/tahoe-lafs/1448/workflows/8486003f-5b86-4e51-879d-e6c8dc44281c/jobs/37927

Nightly image generation is failing because there's been changes in Tor project's Debian package repository:

[...]
Get:6 http://deb.torproject.org/torproject.org stretch InRelease [3528 B]
Ign:6 http://deb.torproject.org/torproject.org stretch InRelease
Get:7 http://deb.torproject.org/torproject.org stretch/main Sources [1244 B]
Get:8 http://deb.torproject.org/torproject.org stretch/main amd64 Packages [3486 B]
Fetched 8258 B in 0s (13.7 kB/s)
Reading package lists...
W: GPG error: http://deb.torproject.org/torproject.org stretch InRelease: The following signatures were invalid: EXPKEYSIG 74A941BA219EC810 deb.torproject.org archive signing key
W: The repository 'http://deb.torproject.org/torproject.org stretch InRelease' is not signed.
+ apt-get --quiet --yes install tor deb.torproject.org-keyring
[...]
WARNING: The following packages cannot be authenticated!
  deb.torproject.org-keyring tor tor-geoipdb
E: There were unauthenticated packages and -y was used without --allow-unauthenticated
The command '/bin/sh -c ${BUILD_SRC_ROOT}/integration/install-tor.sh' returned a non-zero code: 100

[GitHub <noreply@…>]

In b54c7b6/trunk:

Merge pull request #912 from tahoe-lafs/3542.ci-use-new-tor-repo-keys

Use Tor project's new repository signing key

Fixes: ticket:3542