Add support for sentinels (PEP 661) #2031

Job	Run time
Lint	9s
Run tests (3.9)	8s
Run tests (3.9.12)	12s
Run tests (3.10)	9s
Run tests (3.10.4)	12s
Run tests (3.11)	6s
Run tests (3.11.0)	12s
Run tests (3.12)	8s
Run tests (3.12.0)	15s
Run tests (3.13)	6s
Run tests (3.13.0)	14s
Run tests (3.14-dev)	17s
Run tests (pypy3.9)	7s
Run tests (pypy3.10)	13s
Create an issue if daily tests failed	0s
	2m 28s

Provide feedback