Misc. updates to script

[jdavcs]

1. Missing args: I'm sure this is missing in ensure_branches_up_to_date(), the rest is my guess. Otherwise those git commands will be executed against the current directory, which is going to be different when --galaxy-root is passed.
2. Only abort merge if branch was not up-to-date.
3. While testing, I found myself occasionally running this against the wrong branch. I think adding the base branch to the confirmation message may be helpful:

(.venv) rivendell$ galaxy-release-util create-release --galaxy-root ~/0dev/galaxy/_galaxy/dev --new-version 23.2.1 --last-commit 23.1.4
Making sure galaxy clone at '/home/john/0dev/galaxy/_galaxy/dev' is clean:
- Current Galaxy version: 23.2.1.dev0
- New Galaxy version: 23.2.1
- Base branch: release_23.2
Does this look correct? [y/N]:

4. Update CI: remote 3.7 tests, mypy; add 3.12
5. Fix .gitignore to allow local builds (no lib dir here)
6. Cache repo: move github api call out of the loop (was called for each commit); add counter to view progress
7. Handle new packages: if a package has a dev release entry that has no date yet, that dev release may contain some text in the change log (i.e., initial release, first release, etc.), in which case the script would normally raise an error. The script will not raise an error iff (a) the release entry is a dev release; (b) it has no date; and (c) it is the only release entry in the change log (e.g. the "schema" and "tool_shed" packages). In such cases, when updating the package history, the script will not add new PRs to the change log (since there is no "previous" release), but instead will add one bullet point: "First release".
8. Fix bug: don't generate empty bullet points in previous change logs.

I have tested this by using it for creating the 23.2.1 point release.

[mvdbeek]

Feel free to drop the 3.7 tests

[jdavcs]

@mvdbeek did you mean drop 3.7 with mypy and lint? I've added a run under 3.12 with lint and removed mypy altogether - it was giving me too much of a hard time. I don't mind adding it back right away (or, better, after fixing all issues)

[mvdbeek]

Yes, can you please add back mypy to 3.8?