Initial MediaGoblin support for Python 3.10 and 3.11

[Ben Sturmfels]

Hi Folks!

After thoughtlessly upgrading one of my servers to Debian 12, I realised
that MediaGoblin still didn't have Python 3.10/3.11 support. After some
hurried work on it this weekend, and now it does!

All tests are now passing on Debian 12 (Python 3.11) and Ubuntu 22.04
(Python 3.10):

  https://builds.sr.ht/~mediagoblin

Please feel free to try these pre-release updates yourself by upgrading
to the master branch. Refer to the upgrade guide
(https://docs.mediagoblin.org/en/stable/siteadmin/upgrading.html) but
use the following line to switch to the master branch:

  git fetch && git checkout -q master && git pull && git submodule update

If anyone was interested in contributing, further work to upgrade to the
latest Celery 5.3.1 would be amazing! The current 5.1.0 was the most
recent version that would start up without errors on both Python 3.10
and 3.11. Newer versions will pass the test suite, but the Celery
process will fail to start with "AttributeError: 'NoneType' object has
no attribute 'push'".

Regards,
Ben