Replace gcc 12 with gcc 15 in the GitHub action that builds HEMCO on MacOS

[yantosca]

Name and Institution (Required)

Name: Bob Yantosca
Institution: Harvard + GCST

Describe the update

This PR does updates the GitHub Actions configuration file .github/workflows/mac.yml to remove GNU Compiler Collection version 12 (which may no longer be available on HomeBrew) and to replace it with GNU Compiler Collection 15.

Not being able to access GNU Compiler Collection 12 was causing the Mac GitHub action to fail.

Expected changes

This will eliminate the failed GitHub Action on Mac.

[yantosca]

All GEOS-Chem Classic integration tests passed:

==============================================================================
GEOS-Chem Classic: Execution Test Results

CodeDir   : 33d6725 GEOS-Chem update: Merge PR #3131 (Fix vertical flipping for C720)
GEOS-Chem : a3a795878 Merge PR #3131 (Fix vertical flipping of GEOS-FP C720 met fields)
HEMCO     : 43ad195 Merge PR #346 (Replace gcc 12 w/ gcc 15 in Mac GitHub Action )
Cloud-J   : 1dff6fe Merge pull request #31 from geoschem/release/8.0.2
HETP      : 2a99b24 Merge pull request #2 from geoschem/bugfix/initialize_local_variables

Using 24 OpenMP threads
Number of execution tests: 38

Submitted as SLURM job: 50500422
==============================================================================

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%  All execution tests passed!  %%%
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All GEOS-Chem Classic tests were zero-diff w/r/t gcc.14.7.0-alpha.15, except

• gc_4x5_merra2_fullchem_APM
  • Parallelization error (known issue)

All GCHP integration tests passed:

==============================================================================
GCHP: Execution Test Results

CodeDir       : fb61897 Merge PR #529 (Fix vertical flipping c720 fields with processed met)
MAPL          : d1d528e5 Merge pull request #39 from geoschem/feature/mapl_2.55.0
GMAO_Shared   : 4ddb3ec Merge pull request #2 from geoschem/feature/mapl-upgrade
ESMA_cmake    : bd401dc Merge pull request #8 from yuanjianz/gchp/main
FMS           : 259759d Merge pull request #3 from geoschem/feature/update_gmao_libs
FVdycoreCubed : 348620f Merge PR #11 (Scale tracers by pressure ratio in first timestep)
geos-chem     : a3a795878 Merge PR #3131 (Fix vertical flipping of GEOS-FP C720 met fields)
HEMCO         : 43ad195 Merge PR #346 (Replace gcc 12 w/ gcc 15 in Mac GitHub Action )
Cloud-J       : 1dff6fe Merge pull request #31 from geoschem/release/8.0.2
HETP          : 2a99b24 Merge pull request #2 from geoschem/bugfix/initialize_local_variables
GFE           : bac529f Merge pull request #40 from Goddard-Fortran-Ecosystem/feature/mathomp4/update-gftl-1.15.2

Number of execution tests: 12

Submitted as SLURM job: 50500140
==============================================================================
 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%  All execution tests passed!  %%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

All GCHP tests were zero-diff w/r/t gchp.14.7.0-alpha.15.