Add support for sentinels (PEP 661) #2027

Job	Run time
Lint	7s
Run tests (3.9)	8s
Run tests (3.9.12)	10s
Run tests (3.10)	7s
Run tests (3.10.4)	12s
Run tests (3.11)	4s
Run tests (3.11.0)	13s
Run tests (3.12)	6s
Run tests (3.12.0)	16s
Run tests (3.13)	7s
Run tests (3.13.0)	14s
Run tests (3.14-dev)	14s
Run tests (pypy3.9)	9s
Run tests (pypy3.10)	7s
Create an issue if daily tests failed	0s
	2m 14s

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