Support for pickling sentinel objects as singletons #2520

Job	Run time
Run tests (3.11)	14s
Run tests (3.11.0)	23s
Run tests (3.12)	19s
Run tests (3.9)	18s
Run tests (3.10)	18s
Run tests (3.9.12)	18s
Run tests (3.10.4)	20s
Run tests (3.13)	15s
Run tests (pypy3.9)	24s
Run tests (3.14)	19s
Run tests (3.12.0)	19s
Run tests (3.13.0)	21s
Run tests (pypy3.11)	23s
Run tests (pypy3.10)	34s
Create an issue if daily tests failed	-1s
	4m 44s

Provide feedback