ci: Bump Xcode 15.2 to 15.4

[philipphofmann]

Bump Xcode 15.2 to 15.4 for jobs running on macos-14.

Xcode 15.4 is available for macos-14, see https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.468%. Comparing base (65e8a5b) to head (29a0e9d).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4255       +/-   ##
=============================================
- Coverage   91.495%   91.468%   -0.028%     
=============================================
  Files          612       611        -1     
  Lines        49455     49368       -87     
  Branches     17899     17827       -72     
=============================================
- Hits         45249     45156       -93     
- Misses        4113      4120        +7     
+ Partials        93        92        -1     

see 19 files with indirect coverage changes

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