Fix typehint in mask

Author: damusss

buildconfig/stubs/pygame/mask.pyi

@@ -43,7 +43,7 @@ class Mask:
     ) -> Mask: ...
     def connected_component(self, pos: Coordinate = ...) -> Mask: ...
     def connected_components(self, minimum: int = 0) -> List[Mask]: ...
-    def get_bounding_rects(self) -> Rect: ...
+    def get_bounding_rects(self) -> List[Rect]: ...
     def to_surface(
         self,
         surface: Optional[Surface] = None,