Downstream CI: Only use sequential mirgecom runs on Github

  if [[ "$proj_name" = "mirgecom" ]]; then

      # can't turn off MPI in mirgecom

      export CONDA_ENVIRONMENT=conda-env.yml

      if [[ "$GITHUB_ACTIONS" != "" ]]; then

        # Github runners don't have a lot of RAM and tend to run out.

        export CISUPPORT_PARALLEL_PYTEST=no

      fi

      echo "- mpi4py" >> "$CONDA_ENVIRONMENT"

  else

      sed -i "/mpi4py/ d" requirements.txt