stop requesting x64 for mac to work on arm

[m-reuter]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 6.95%. Comparing base (ae82e8a) to head (961d44b).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #34      +/-   ##
========================================
- Coverage   7.26%   6.95%   -0.32%     
========================================
  Files          5       5              
  Lines        633     633              
  Branches      77      77              
========================================
- Hits          46      44       -2     
- Misses       585     586       +1     
- Partials       2       3       +1     

Flag	Coverage Δ
unittests	6.95% <ø> (-0.32%)	⬇️

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[m-reuter]

I had issues with PyQt6 (for the documentation build with sphinx for unknown reasons), so I went back to PyQt5, but without specifying the exact version 5.15.6 that we pinned before. This older version is not available on all runners. I do not know why that version was explicitly requested.