GHA: Use GCC 13 for coverage

[Flamefire]

For testing

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.52%. Comparing base (675b6f2) to head (f4d7a9c).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #242      +/-   ##
===========================================
- Coverage    95.81%   95.52%   -0.30%     
===========================================
  Files          117      117              
  Lines        10353    10665     +312     
===========================================
+ Hits          9920    10188     +268     
- Misses         433      477      +44     

see 66 files with indirect coverage changes

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