Add action to install MPI

Author: matteobachetti

.github/workflows/ci_test.yml

@@ -152,6 +152,11 @@ jobs:
         python -c "import pip; print(f'pip {pip.__version__}')"
         python -c "import setuptools; print(f'setuptools {setuptools.__version__}')"
         python -c "import tox; print(f'tox {tox.__version__}')"
+    - name: Setup MPI
+      if: "contains(matrix.tox_env, 'alldeps')"
+      uses: mpi4py/setup-mpi@v1
+      with:
+          mpi: "openmpi"
     - name: Run tests
       if: "! matrix.use_remote_data"
       run: tox -e ${{ matrix.tox_env }}