fix typo

Co-authored-by: Stanislav Terliakov <50529348+sterliakov@users.noreply.github.com>

Author: tyralla

mypy/errors.py

@@ -286,7 +286,7 @@ def yield_uselessness_error_infos(self) -> Iterator[tuple[str, Context, ErrorCod
     def yield_nonoverlapping_types(
         self,
     ) -> Iterator[tuple[tuple[list[Type], list[Type]], str, Context]]:
-        """Report expressions were non-overlapping types were detected for all iterations
+        """Report expressions where non-overlapping types were detected for all iterations
         were the expression was reachable."""
 
         selected = set()