Review: Add Python 3.11 and 3.12 to the testing

[cclauss]

https://devguide.python.org/versions/

This is still Django v4 but not yet v5.

[JoelLefkowitz]

Hey @cclauss thanks for raising this, could you please update the envlist in the tox.ini file too for the newer versions of python? Also we need to keep the version 3.6 run in the version matrix as it's required by the branch protection rules for this repo and cannot be removed without the original author of the repo.

[cclauss]

A lot of the changes in this PR are about supporting Python 3.7. Should we stop supporting it and treat it like we do Py36?

Should we drop Py3.8 which is also EOL?

Should we drop Django < 4.2 which are also EOL?

[JoelLefkowitz]

A lot of the changes in this PR are about supporting Python 3.7. Should we stop supporting it and treat it like we do Py36?

Should we drop Py3.8 which is also EOL?

Should we drop Django < 4.2 which are also EOL?

Since we don't have any reliable feedback from the users on what versions they are using I'd like to keep supporting as many versions as we can. Since this is quite a mature package I'd like to prioritise stability