Update mypy 0.750 -> 0.761

This fixes some type: ignores due to typeshed update.

Newer mypy seem to ignore unannotated functions better, so add a few
minor annotations so that existing correct type:ignores make sense.

src/_pytest/_code/source.py

@@ -339,9 +339,7 @@ def getstatementrange_ast(
         block_finder.started = source.lines[start][0].isspace()
         it = ((x + "\n") for x in source.lines[start:end])
         try:
-            # Type ignored until next mypy release.
-            # https://github.com/python/typeshed/commit/c0d46a20353b733befb85d8b9cc24e5b0bcd8f9a
-            for tok in tokenize.generate_tokens(lambda: next(it)):  # type: ignore
+            for tok in tokenize.generate_tokens(lambda: next(it)):
                 block_finder.tokeneater(*tok)
         except (inspect.EndOfBlock, IndentationError):
             end = block_finder.last + start