Fix wrong defval in EditorSpatialGizmo.add_mesh method bind

The type of the parameter 'skeleton' was changed from 'RID' to 'SkinReference', yet the default value remained 'RID()'.

editor/spatial_editor_gizmos.cpp

@@ -729,7 +729,7 @@ void EditorSpatialGizmo::set_plugin(EditorSpatialGizmoPlugin *p_plugin) {
 void EditorSpatialGizmo::_bind_methods() {
 
 	ClassDB::bind_method(D_METHOD("add_lines", "lines", "material", "billboard"), &EditorSpatialGizmo::add_lines, DEFVAL(false));
-	ClassDB::bind_method(D_METHOD("add_mesh", "mesh", "billboard", "skeleton", "material"), &EditorSpatialGizmo::add_mesh, DEFVAL(false), DEFVAL(RID()), DEFVAL(Variant()));
+	ClassDB::bind_method(D_METHOD("add_mesh", "mesh", "billboard", "skeleton", "material"), &EditorSpatialGizmo::add_mesh, DEFVAL(false), DEFVAL(Variant()), DEFVAL(Variant()));
 	ClassDB::bind_method(D_METHOD("add_collision_segments", "segments"), &EditorSpatialGizmo::add_collision_segments);
 	ClassDB::bind_method(D_METHOD("add_collision_triangles", "triangles"), &EditorSpatialGizmo::add_collision_triangles);
 	ClassDB::bind_method(D_METHOD("add_unscaled_billboard", "material", "default_scale"), &EditorSpatialGizmo::add_unscaled_billboard, DEFVAL(1));