compiler: fix msd thickness lowering #287

Job	Run time
pytest-mpi (pytest-mpi-docker-icx)	36m 32s
pytest-mpi (pytest-mpi-docker-gcc-arm)	24m 9s
pytest-mpi (3.10)	44m 28s
pytest-mpi (3.11)	44m 18s
pytest-mpi (pytest-mpi-docker-gcc)	33m 34s
	3h 3m 1s

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