Use correct type annotation for .filter_errors (#13486)

The same as ErrorWatcher constructor.

Author: sobolevn

mypy/messages.py

@@ -162,7 +162,10 @@ def __init__(self, errors: Errors, modules: dict[str, MypyFile]) -> None:
     #
 
     def filter_errors(
-        self, *, filter_errors: bool = True, save_filtered_errors: bool = False
+        self,
+        *,
+        filter_errors: bool | Callable[[str, ErrorInfo], bool] = True,
+        save_filtered_errors: bool = False,
     ) -> ErrorWatcher:
         return ErrorWatcher(
             self.errors, filter_errors=filter_errors, save_filtered_errors=save_filtered_errors