Bump min Python version for GHA (and fix spurious CI error) #5767

Job	Run time
collateral (diffcov)	5m 44s
test (3.9, ubuntu-latest)	4m 32s
test_cygwin (39, windows-latest)	17m 29s
test (3.9, macos-latest)	3m 37s
collateral (docs)	1m 50s
test (3.9, windows-latest)	10m 0s
test (3.13, ubuntu-latest)	5m 27s
test (3.13, macos-latest)	4m 17s
test (3.13, windows-latest)	13m 58s
test (3.10, ubuntu-latest)	4m 10s
test (3.11, ubuntu-latest)	3m 52s
test (3.12, ubuntu-latest)	5m 47s
test (3.14, ubuntu-latest)	6m 28s
test (pypy3.10, ubuntu-latest, stdlib)	16m 32s
test (ubuntu-latest, 3.10, stdlib)	4m 6s
integration-test	0s
check	3s
release	0s
	1h 47m 52s

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