mypy

Tachyon: Fix unesecarry plural when there is a single file/sample (#1… #18378

Job	Run time
Run mypy on Lib/test/libregrtest	19s
Run mypy on Tools/cases_generator	15s
Run mypy on Tools/clinic	18s
Run mypy on Lib/_pyrepl	18s
Run mypy on Lib/tomllib	21s
Run mypy on Tools/peg_generator	20s
Run mypy on Tools/build	20s
Run mypy on Tools/jit	23s
	2m 34s

Provide feedback