mpi: Avoid UnboundLocalVariable error #6691

Job	Run time
pytest-ubuntu-py311-gcc11-noomp-base	33m 25s
pytest-ubuntu-py311-gcc11-noomp-adjoint	28m 9s
pytest-ubuntu-py38-gcc12-omp-base	33m 25s
pytest-ubuntu-py38-gcc12-omp-adjoint	27m 28s
pytest-ubuntu-py38-gcc7-omp-base	32m 15s
pytest-ubuntu-py38-gcc7-omp-adjoint	27m 37s
pytest-ubuntu-py310-gcc10-noomp-base	33m 9s
pytest-ubuntu-py310-gcc10-noomp-adjoint	28m 6s
pytest-ubuntu-py312-gcc13-omp-base	43m 55s
pytest-ubuntu-py312-gcc13-omp-adjoint	36m 28s
pytest-ubuntu-py39-gcc9-omp-base	32m 12s
pytest-ubuntu-py39-gcc9-omp-adjoint	27m 19s
pytest-osx-py312-clang-omp-base	1m 25s
pytest-docker-py39-gcc-omp-base	33m 36s
pytest-docker-py39-gcc-omp-adjoint	25m 19s
pytest-docker-py39-icx-omp-base	27m 21s
pytest-docker-py39-icx-omp-adjoint	25m 53s
	8h 17m 2s

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