Bump actions/checkout from 3 to 4 #61

Job	Run time
1/4	27m 22s
2/4	22m 15s
3/4	29m 37s
4/4	22m 57s
py-3.11	23m 11s
flaky	9m 27s
_remote_background_indep_poll	9m 57s
_remote_background_indep_tcp	13m 24s
macos 1/5	22m 29s
macos 2/5	18m 3s
codecov	7s
	3h 18m 49s

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