typing: Gtk4: Makes Child Template type generic (#187)

src/gi-stubs/repository/_Gtk4.pyi

@@ -29093,7 +29093,8 @@ class Template:
         def __init__(self, name: str = ...) -> None: ...
         def __call__(self, func: Callable[..., Any]) -> Any: ...
 
-    class Child: ...
+    @classmethod
+    def Child() -> Any: ...
 
 class Text(Widget, Accessible, AccessibleText, Buildable, ConstraintTarget, Editable):
     """