mypy

GH-137059: `url2pathname()`: fix support for drive letter in netloc (… #15920

Job	Run time
Run mypy on Lib/test/libregrtest	15s
Run mypy on Tools/build	16s
Run mypy on Lib/tomllib	16s
Run mypy on Tools/cases_generator	19s
Run mypy on Lib/_pyrepl	17s
Run mypy on Tools/jit	17s
Run mypy on Tools/clinic	19s
Run mypy on Tools/peg_generator	21s
	2m 20s

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