Add support for sentinels (PEP 661) (#594) #2033

Job	Run time
Lint	12s
Run tests (3.9)	11s
Run tests (3.9.12)	15s
Run tests (3.10)	16s
Run tests (3.10.4)	13s
Run tests (3.11)	9s
Run tests (3.11.0)	13s
Run tests (3.12)	8s
Run tests (3.12.0)	16s
Run tests (3.13)	10s
Run tests (3.13.0)	17s
Run tests (3.14-dev)	16s
Run tests (pypy3.9)	20s
Run tests (pypy3.10)	27s
Create an issue if daily tests failed	0s
	3m 23s

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