CI: test 3.13 on the CI

[superlopuh]

uv venv picks the newest Python available, and 3.13 seems to be failing for me locally. This is a problem with an easy workaround (pick an older Python), but I'd rather we just worked out of the box. I'll look into how to actually fix it in the next few days, help would be appreciated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.08%. Comparing base (163fde2) to head (cb9520f).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3346      +/-   ##
==========================================
+ Coverage   90.06%   90.08%   +0.02%     
==========================================
  Files         446      446              
  Lines       56382    56419      +37     
  Branches     5409     5417       +8     
==========================================
+ Hits        50779    50824      +45     
+ Misses       4177     4162      -15     
- Partials     1426     1433       +7     

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