Replace macos-12 with 15

[mborland]

macOS-12 is pending removal and 15 was just added

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.1%. Comparing base (8274270) to head (450d564).
Report is 14 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #755     +/-   ##
=========================================
+ Coverage     99.1%   99.1%   +0.1%     
=========================================
  Files          227     227             
  Lines        16863   16863             
  Branches      1816    1816             
=========================================
+ Hits         16708   16709      +1     
+ Misses         155     154      -1     

see 1 file with indirect coverage changes

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