feat(ci): run tests on macos

[nijel]

This would allow to catch issues like #14019 earlier.

[nijel]

Even after #14032 there is one failure in the Selenium tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.01%. Comparing base (c35fa9e) to head (4c0c19a).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14023      +/-   ##
==========================================
- Coverage   91.01%   91.01%   -0.01%     
==========================================
  Files         608      608              
  Lines       63639    63647       +8     
  Branches     6584     6584              
==========================================
+ Hits        57920    57927       +7     
  Misses       4026     4026              
- Partials     1693     1694       +1     

Files with missing lines	Coverage Δ
weblate/trans/tests/test_selenium.py	95.78% <100.00%> (+0.04%)	⬆️

... and 1 file with indirect coverage changes