Fix type of of optparse.Option's _{check,set}_opt_strings() methods (#3895)

Author: dlax

stdlib/2and3/optparse.pyi

@@ -111,10 +111,10 @@ class Option:
     def _check_const(self) -> None: ...
     def _check_dest(self) -> None: ...
     def _check_nargs(self) -> None: ...
-    def _check_opt_strings(self, opts: Optional[_Text]) -> Any: ...
+    def _check_opt_strings(self, opts: Iterable[Optional[_Text]]) -> List[_Text]: ...
     def _check_type(self) -> None: ...
     def _set_attrs(self, attrs: Dict[_Text, Any]) -> None: ...
-    def _set_opt_strings(self, opts: _Text) -> None: ...
+    def _set_opt_strings(self, opts: Iterable[_Text]) -> None: ...
     def check_value(self, opt: Any, value: Any) -> Any: ...
     def convert_value(self, opt: Any, value: Any) -> Any: ...
     def get_opt_string(self) -> _Text: ...