Modified (temporarily) MPI CI workflow to add branches that permit adding mg tests

Author: principejavier

.github/workflows/ci_mpi.yml

@@ -77,6 +77,9 @@ jobs:
         run: |
           using Pkg
           Pkg.add("MPIPreferences")
+          Pkg.add("Gridap#polytopal")
+          Pkg.add("GridapDistributed#polytopal")
+          Pkg.add("GridapSolvers#develop")
       - name: use MPI system binary 
         shell: julia --color=yes --project=. {0}
         run: |