tests

Enable mypy on CI #4000

Job	Run time
collateral (diffcov)	6m 18s
test_cygwin (39, windows-latest)	13m 22s
test (3.8, ubuntu-latest)	4m 1s
collateral (docs)	1m 10s
test (3.8, macos-latest)	7m 34s
test (3.8, windows-latest)	9m 20s
test (3.11, ubuntu-latest)	3m 52s
test (3.11, macos-latest)	5m 38s
test (3.11, windows-latest)	9m 33s
test (3.12, ubuntu-latest)	6m 59s
test (3.12, macos-latest)	8m 2s
test (3.12, windows-latest)	9m 36s
test (3.9, ubuntu-latest)	4m 23s
test (3.10, ubuntu-latest)	4m 16s
test (pypy3.10, ubuntu-latest, stdlib)	9m 31s
test (ubuntu-latest, 3.10, stdlib)	4m 17s
integration-test	0s
check	1s
release	0s
	1h 47m 53s

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