[godot] Fix property editor not returning true on handling animation mixes.

spine-godot/example/assets/spineboy/spinebody-data-res.tres

@@ -5,7 +5,7 @@
 
 [sub_resource type="SpineAnimationMix" id=1]
 from = "idle"
-to = "death"
+to = "run"
 mix = 1.0
 
 [sub_resource type="SpineAnimationMix" id=2]

spine-godot/spine_godot/SpineEditorPlugin.cpp

@@ -94,6 +94,7 @@ bool SpineSkeletonDataResourceInspectorPlugin::parse_property(Object *object, Va
 		auto mixes_property = memnew(SpineEditorPropertyAnimationMixes);
 		mixes_property->setup(skeleton_data);
 		add_property_editor(path, mixes_property);
+		return true;
 	}
 	return false;
 }