Replace Flake8-2020 by Ruff #3932

Job	Run time
test_cygwin (39, windows-latest)	13m 51s
test (3.8, ubuntu-latest)	4m 15s
collateral (diffcov)	6m 24s
test (3.8, macos-latest)	9m 50s
collateral (docs)	56s
test (3.8, windows-latest)	9m 1s
test (3.11, ubuntu-latest)	3m 53s
test (3.11, macos-latest)	6m 30s
test (3.11, windows-latest)	9m 57s
test (3.12, ubuntu-latest)	6m 40s
test (3.12, macos-latest)	8m 16s
test (3.12, windows-latest)	11m 23s
test (3.9, ubuntu-latest)	4m 3s
test (3.10, ubuntu-latest)	3m 53s
test (pypy3.10, ubuntu-latest, stdlib)	6m 31s
test (ubuntu-latest, 3.10, stdlib)	4m 12s
integration-test	0s
check	1s
release	0s
	1h 49m 36s

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