Support Python 3.13 and test on it
- Path is no longer a context manager (this already didn't do anything, but is an actual error in 3.13) https://docs.python.org/3/whatsnew/3.13.html#id4
- Path.glob('**') is no longer directories-only - use "**/" for that https://docs.python.org/3/whatsnew/3.13.html#pathlib
- Add 3.13 to CI
(While we're looking at the CI setup: 'python-slim-bullseye' should probably be 'python-slim-bookworm', but this doesn't actually make that change.)
Edited by Rebecca N. Palmer