require mpi4py v4 (#1052) #8838

Job	Run time
Mypy	4m 13s
Documentation	5m 7s
Emirge installation (ubuntu-latest)	5m 30s
Flake8	16s
Examples (ubuntu-latest)	55m 27s
Emirge installation (macos-latest)	7m 27s
Examples (porter)	1h 19m 4s
Production testing (ubuntu-latest)	1h 54m 8s
Production testing (macos-latest)	1h 26m 35s
Production testing (porter)	1h 9m 4s
pydocstyle	11s
Pylint	4m 7s
Pytest	2h 27m 49s
	9h 38m 58s

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