Add test jobs for Python on MPI-GROMACS
Spread the Python version coverage across OpenMPI and thread-MPI GROMACS installations.
Refs #3563 (closed)
Without a resolution to #4422 (closed) / #4423 (closed), the tests against MPI-GROMACS with mpiexec -n 2
cannot pass. I can either add some logic to skip this particular case until a fix for #4422 (closed) / #4423 (closed) is asserted (e.g. pytest.mark.skip_if(not gmxapi.version.has_feature('4423-fix'))
) or this MR can be combined with the MR that provides the #4422 (closed) solution.