TST: add explicit support for CPython 3.12 and 3.13

[neutrinoceros]

based off #672

[neutrinoceros]

no problems here. This should be undrafted once #672 is merged

[neutrinoceros]

Actually I would still recommend to wait a bit to merge this one:

• resources to run the test suite are limited and this increases demand. Given how long the full suite is to run and how many PRs I'd like to get going, merging this one early could slow down the whole process significantly
• no errors so far, but warnings are not being treated as errors yet, so there might still be deprecation warning slipping in, and it'd be best to solve them here

[IainHammond]

Looks good to me! Just needs the readme to be updated on line 9 I assume? Something like this: https://img.shields.io/badge/Python-3.10%2C%203.11%2C%203.12%2C%203.13-brightgreen.svg

[neutrinoceros]

good catch. Done

[VChristiaens]

Thanks a lot! This looks good to me.