Enable install & testing against Python 3.12

[neiljp]

What does this PR do, and why?

This PR is intended to

• check that dependencies work satisfactorily under Python 3.12
• ensure that we install under Python 3.12

These also enabled confirmation that after the 0.2.0/0.2.1 release yanks, that installing under an unsupported python does not install a very old option any more :+1:

NOTE: This does not guarantee that there are no issues with python 3.12. For that we likely need urwid 2.2+ (http://urwid.org/changelog.html#release-2-2-0), however that also removes python 3.7 compatibility.

Outstanding aspect(s)

• [x] Wait for Python 3.12 release
• [x] Ensure that dependencies install OK
• [x] Tests run OK against the release?
• [ ] Manual testing?

External discussion & connections

• [ ] Discussed in #zulip-terminal in topic
• [ ] Fully fixes #
• [ ] Partially fixes issue #
• [ ] Builds upon previous unmerged work in PR #
• [ ] Is a follow-up to work in PR #
• [ ] Requires merge of PR #
• [ ] Merge will enable work on #

How did you test this?

• [ ] Manually - Behavioral changes
• [ ] Manually - Visual changes
• [ ] Adapting existing automated tests
• [ ] Adding automated tests for new behavior (or missing tests)
• [ ] Existing automated tests should already cover this (only a refactor of tested code)

Self-review checklist for each commit

• [ ] It is a minimal coherent idea
• [ ] It has a commit summary following the documented style (title & body)
• [ ] It has a commit summary describing the motivation and reasoning for the change
• [ ] It individually passes linting and tests
• [ ] It contains test additions for any new behavior
• [ ] It flows clearly from a previous branch commit, and/or prepares for the next commit