mypy

InternalDocs: Correct struct path for latin1 singletons in `string_in… #20672

Job	Run time
Run mypy on Tools/check-c-api-docs	18s
Run mypy on Lib/test/libregrtest	23s
Run mypy on Tools/cases_generator	20s
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/peg_generator	17s
Run mypy on Tools/build	20s
Run mypy on Lib/tomllib	18s
Run mypy on Tools/jit	18s
Run mypy on Tools/clinic	20s
	2m 53s

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