Fix typo in documentation_MPI.ipynb #1534

Job	Run time
cache-pixi-lock / Generate output	45s
Unit tests: ubuntu \| pixi run -e test-latest tests	2m 38s
Unit tests: ubuntu \| pixi run -e test-py311 tests	2m 11s
Integration: ${{ matrix.os }} \| pixi run -e ${{ matrix.pixi-environment }} tests-notebooks	0s
TypeChecking: pixi run typing	-1s
merge-test-artifacts	0s
cache-pixi-lock / Generate output	45s
Unit tests: ubuntu \| pixi run -e test-py311 tests	2m 11s
Integration: ${{ matrix.os }} \| pixi run -e ${{ matrix.pixi-environment }} tests-notebooks	-3193s
TypeChecking: pixi run typing	-3193s
Unit tests: ubuntu \| pixi run -e test-latest tests	2m 38s
merge-test-artifacts	-1s
	-5720s

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