New CircleCI/deps failure

[namurphy]

I noticed a recent CI failure whilst working on #142 for circleci/deps. Several checks were subsequently skipped (testpostgres, testpostgres3, unittest3, unittest, and docs).

I'm wondering if it would be most sensible to port CI to GitHub Actions (#134) rather than updating CircleCI. 🤔

Details

The circleci/deps check failed with the following output:

Ign:1 http://deb.debian.org/debian buster InRelease
Ign:2 http://deb.debian.org/debian buster-updates InRelease
Err:3 http://deb.debian.org/debian buster Release          
  404  Not Found [IP: 146.75.30.132 80]
Err:4 http://deb.debian.org/debian buster-updates Release  
  404  Not Found [IP: 146.75.30.132 80]
Ign:5 http://security.debian.org/debian-security buster/updates InRelease
Err:6 http://security.debian.org/debian-security buster/updates Release
  404  Not Found [IP: 146.75.30.132 80]
Reading package lists... Done
E: The repository 'http://deb.debian.org/debian buster Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://deb.debian.org/debian buster-updates Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://security.debian.org/debian-security buster/updates Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

[jtniehof]

Yes, we absolutely need to just get to GHA. Merging #137 first will bring us a little further into the 21st century and probably make that more straightforward.