use gfortran-15 via FC environment variable on macos

[mattip]

• I updated the package version in pyproject.toml and made sure the first 3 numbers match git describe --tags --abbrev=8 in OpenBLAS at the OPENBLAS_COMMIT. If I did not update OPENBLAS_COMMIT, I incremented the wheel build number (i.e. 0.3.29.0.0 to 0.3.29.0.1)

The alias gfortran=gfortran-15 did not work, as seen in the line OpenBLAS: Detecting fortran compiler failed. Can only compile BLAS and f2c-converted LAPACK hidden deep in the logs. I think this is because the alias does not pass command line arguments.

[mattip]

This is duplicating much of #237, closing in favor of iterating on that