ci: use Python 3.14 more

[flying-sheep]

See scverse/cookiecutter-scverse#462

Also just use 3.14 as default test version, since a stable 3.14-compatible numba has been released.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.01%. Comparing base (3cf6391) to head (ff439bf).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3936      +/-   ##
==========================================
+ Coverage   76.93%   78.01%   +1.07%     
==========================================
  Files         117      117              
  Lines       12460    12466       +6     
==========================================
+ Hits         9586     9725     +139     
+ Misses       2874     2741     -133     

Flag	Coverage Δ
hatch-test.low-vers	77.33% <100.00%> (?)
hatch-test.pre	76.96% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/scanpy/external/pl.py	31.52% <100.00%> (-2.17%)	⬇️
src/scanpy/external/pp/__init__.py	100.00% <100.00%> (ø)
src/scanpy/external/pp/_harmony_integrate.py	50.00% <ø> (-2.95%)	⬇️
src/scanpy/plotting/_tools/scatterplots.py	83.52% <100.00%> (+0.39%)	⬆️

... and 8 files with indirect coverage changes