[punq] Add missing return type for Container.register() (#15301)

stubs/punq/punq/__init__.pyi

@@ -86,7 +86,7 @@ class Container:
         instance: _T | _Empty = ...,
         scope: Scope = Scope.transient,
         **kwargs: Any,
-    ): ...
+    ) -> Container: ...
     def resolve_all(self, service: type[_T] | str, **kwargs: Any) -> list[_T]: ...
     def resolve(self, service_key: type[_T] | str, **kwargs: Any) -> _T: ...
     def instantiate(self, service_key: type[_T] | str, **kwargs: Any) -> _T: ...