Fix typos in `TypeIs` docstring #1717

Job	Run time
Lint	6s
Run tests (3.8)	8s
Run tests (3.8.0)	12s
Run tests (3.9)	5s
Run tests (3.9.0)	9s
Run tests (3.10)	4s
Run tests (3.10.0)	10s
Run tests (3.11)	6s
Run tests (3.11.0)	16s
Run tests (3.12)	6s
Run tests (3.12.0)	13s
Run tests (3.13)	16s
Run tests (3.13.0)	13s
Run tests (pypy3.8)	9s
Run tests (pypy3.9)	12s
Run tests (pypy3.10)	7s
Create an issue if daily tests failed	0s
	2m 32s

Provide feedback