mypy

gh-138372: Fix SyntaxWarning for erroneous t-string subscription (#13… #9550

Job	Run time
Run mypy on Lib/test/libregrtest	17s
Run mypy on Lib/tomllib	18s
Run mypy on Lib/_pyrepl	17s
Run mypy on Tools/build	15s
Run mypy on Tools/cases_generator	16s
Run mypy on Tools/peg_generator	16s
Run mypy on Tools/jit	20s
Run mypy on Tools/clinic	21s
	2m 20s

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