Issue with setup-fortran and setup-fpm on macOS

[gha3mi]

@wpbonelli, please check this out: https://github.com/gha3mi/test-setup-fortran/actions/runs/8079049989

It appears that the issue is resolved when gcc@10 is installed alongside the desired compiler on macOS. The issue seems to be that fpm looks for gcc@10. I believe this may not be a problem with setup-fortran, but rather with fpm or setup-fpm in terms of how the binary files are provided. It seems setup-fpm downloads the latest binary files from fpm, but fpm is compiled with gcc@10.