mypy

gh-137390: Add missing line continuation character in configure.ac (#… #9449

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

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