run unit tests on 3.8 only for Mac OS vs. both 3.8 and 3.9 (#19889)
run unit tests on 3.8 only for Mac OS vs. both 3.8 and 3.9 (#19889)


LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack,LLNL/spack