Add support for sentinels (PEP 661) #2010

Job	Run time
Lint	6s
Run tests (3.9)	5s
Run tests (3.9.12)	13s
Run tests (3.10)	7s
Run tests (3.10.4)	11s
Run tests (3.11)	6s
Run tests (3.11.0)	12s
Run tests (3.12)	9s
Run tests (3.12.0)	17s
Run tests (3.13)	6s
Run tests (3.13.0)	13s
Run tests (3.14-dev)	16s
Run tests (pypy3.9)	12s
Run tests (pypy3.10)	9s
Create an issue if daily tests failed	0s
	2m 22s

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