typing: Gtk3: Improve hints

Author: buzz

src/gi-stubs/repository/_Gtk3.pyi

@@ -63822,8 +63822,10 @@ class TreeModelRow:
     def __getitem__(self, key: int) -> Any: ...
     def __setitem__(self, key: int, value: Any) -> None: ...
 
+# override
 class TreeModelRowIter:
-    def next(self): ...  # FIXME Function
+    def next(self) -> TreeModelRow: ...
+    def __next__(self) -> TreeModelRow: ...
 
 class TreeModelSort(GObject.Object, TreeDragSource, TreeModel, TreeSortable):
     """