mypy

gh-84116: Add missing backslash to `_SubParsersAction.add_parser` sig… #19426

Job	Run time
Run mypy on Tools/cases_generator	17s
Run mypy on Tools/build	19s
Run mypy on Tools/check-c-api-docs	17s
Run mypy on Lib/tomllib	15s
Run mypy on Tools/jit	17s
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/clinic	20s
Run mypy on Lib/_pyrepl	21s
Run mypy on Tools/peg_generator	24s
	2m 49s

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