Candidate fix for MPI hang CI job

Author: hughcars

.github/workflows/build-and-test-linux.yml

@@ -128,11 +128,11 @@ jobs:
           with-solver: strumpack
         - arch: arm
           compiler: clang
-          mpi: mpich
+          mpi: openmpi
           math-libs: armpl
           build-shared: shared
           with-64bit-int: int32
-          with-openmp: serial # openmp -- mumps 5.8.0 introduces hang possibility
+          with-openmp: openmp
           with-eigensolver: arpack
           with-solver: mumps
         - arch: arm