🩹 make sure to define Py_GIL_DISABLED on Windows for Python 3.13t

[burgholzer]

Description

As pointed out in pypa/cibuildwheel#1975 (comment) free-threading (Python 3.13t) builds on Windows need to have Py_GIL_DISABLED set in order to properly work.
This PR ensures that the corresponding setting is always set.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.2%. Comparing base (a0a61e2) to head (adbfeed).
Report is 83 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #452     +/-   ##
=======================================
- Coverage   95.3%   95.2%   -0.1%     
=======================================
  Files         40      40             
  Lines       1837    1837             
  Branches     224     224             
=======================================
- Hits        1751    1750      -1     
- Misses        86      87      +1     

Flag	Coverage Δ
cpp	95.6% <ø> (-0.1%)	⬇️
python	93.7% <ø> (ø)

see 1 file with indirect coverage changes