3.1.37 - a proper fix CVE-2023-41040

@EliahKagan

What's Changed

Improve Python version and OS compatibility, fixing deprecations by @EliahKagan in #1654
Better document env_case test/fixture and cwd by @EliahKagan in #1657
Remove spurious executable permissions by @EliahKagan in #1658
Fix up checks in Makefile and make them portable by @EliahKagan in #1661
Fix URLs that were redirecting to another license by @EliahKagan in #1662
Assorted small fixes/improvements to root dir docs by @EliahKagan in #1663
Use venv instead of virtualenv in test_installation by @EliahKagan in #1664
Omit py_modules in setup by @EliahKagan in #1665
Don't track code coverage temporary files by @EliahKagan in #1666
Configure tox by @EliahKagan in #1667
Format tests with black and auto-exclude untracked paths by @EliahKagan in #1668
Upgrade and broaden flake8, fixing style problems and bugs by @EliahKagan in #1673
Fix rollback bug in SymbolicReference.set_reference by @EliahKagan in #1675
Remove @NoEffect annotations by @EliahKagan in #1677
Add more checks for the validity of refnames by @facutuesca in #1672

Full Changelog: 3.1.36...3.1.37