Reraise sensible errors from auto_chmod #5409

Job	Run time
test_cygwin (39, windows-latest)	18m 22s
collateral (diffcov)	5m 14s
collateral (docs)	1m 53s
test (3.8, ubuntu-latest)	4m 2s
test (3.8, windows-latest)	10m 53s
test (3.12, ubuntu-latest)	5m 9s
test (3.12, macos-latest)	5m 11s
test (3.12, windows-latest)	18m 13s
test (3.9, ubuntu-latest)	4m 10s
test (3.10, ubuntu-latest)	3m 54s
test (3.11, ubuntu-latest)	3m 52s
test (pypy3.10, ubuntu-latest, stdlib)	12m 9s
test (ubuntu-latest, 3.10, stdlib)	3m 47s
test (3.8, macos-13)	6m 26s
integration-test	0s
check	3s
release	0s
	1h 43m 18s

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