Add support for sentinels (PEP 661) #2014

Job	Run time
Lint	7s
Run tests (3.9)	6s
Run tests (3.9.12)	11s
Run tests (3.10)	6s
Run tests (3.10.4)	13s
Run tests (3.11)	8s
Run tests (3.11.0)	12s
Run tests (3.12)	7s
Run tests (3.12.0)	14s
Run tests (3.13)	6s
Run tests (3.13.0)	13s
Run tests (3.14-dev)	14s
Run tests (pypy3.9)	10s
Run tests (pypy3.10)	10s
Create an issue if daily tests failed	0s
	2m 17s

Provide feedback