Test on Python 3.13-dev

[RatanShreshtha]

Python 3.13.0rc2 was made available recently: https://github.com/actions/python-versions/releases/tag/3.13.0-rc.2-10765745850

[Schefflera-Arboricola]

Thank you @RatanShreshtha :)

[dschult]

This looks like the tests are passing just fine!

It's only a week until the expected release date for 3.13.
Let's be sure to update it to 3.13 once that release occurs.

Thanks very much!