mypy

gh-145546: unittest.util: fix `sorted_list_difference` tail deduplica… #19885

Job	Run time
Run mypy on Lib/tomllib	18s
Run mypy on Lib/_pyrepl	19s
Run mypy on Tools/build	21s
Run mypy on Tools/jit	19s
Run mypy on Tools/clinic	18s
Run mypy on Tools/check-c-api-docs	17s
Run mypy on Tools/peg_generator	20s
Run mypy on Tools/cases_generator	16s
Run mypy on Lib/test/libregrtest	19s
	2m 47s

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