Fix type in argparse.HelpFormatter._fill_text() (#3229)

Author: jjmortensen

stdlib/2and3/argparse.pyi

@@ -225,7 +225,7 @@ class HelpFormatter:
     def _expand_help(self, action: Action) -> _Text: ...
     def _iter_indented_subactions(self, action: Action) -> Generator[Action, None, None]: ...
     def _split_lines(self, text: Text, width: int) -> List[_Text]: ...
-    def _fill_text(self, text: Text, width: int, indent: int) -> _Text: ...
+    def _fill_text(self, text: Text, width: int, indent: Text) -> _Text: ...
     def _get_help_string(self, action: Action) -> Optional[_Text]: ...
     def _get_default_metavar_for_optional(self, action: Action) -> _Text: ...
     def _get_default_metavar_for_positional(self, action: Action) -> _Text: ...