Support for pickling sentinel objects as singletons #2086

Job	Run time
Lint	5s
Run tests (3.9)	5s
Run tests (3.9.12)	16s
Run tests (3.10)	8s
Run tests (3.10.4)	12s
Run tests (3.11)	6s
Run tests (3.11.0)	16s
Run tests (3.12)	5s
Run tests (3.12.0)	13s
Run tests (3.13)	4s
Run tests (3.13.0)	16s
Run tests (3.14)	14s
Run tests (pypy3.9)	12s
Run tests (pypy3.10)	10s
Create an issue if daily tests failed	0s
	2m 22s

Provide feedback