mypy

gh-106318: Fix incorrectly rendered code block in `str.isalnum()` doc… #19498

Job	Run time
Run mypy on Tools/jit	18s
Run mypy on Lib/_pyrepl	17s
Run mypy on Lib/tomllib	17s
Run mypy on Tools/clinic	19s
Run mypy on Tools/check-c-api-docs	19s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/build	21s
Run mypy on Tools/peg_generator	20s
Run mypy on Tools/cases_generator	18s
	2m 48s

Provide feedback