### Godot version

Master (4.2)

### System information

Windows 11 - Vulkan - Nvidia RTX 4070 - intel i5 13600KF

### Issue description

As you can see in the video when you try to add multiple scenes in to the 3D viewport (only with multiple scenes) the editor throws this error.

```
ERROR: Can't add child '@Node3D@18837' to '@SubViewport@9274', already has a parent '@SubViewport@9274'.
   at: (scene\main\node.cpp:1411)
```


Video: https://youtu.be/BVcCIigQJDw

This happens in the latest master (pulled on 2.11.2023).

### Steps to reproduce

Drag couple of the 3d mesh scenes into the 3D viewport and then select multiple scenes and drag them over and observer the error.

### Minimal reproduction project

[TestSceneDragAndDrop.zip](https://github.com/godotengine/godot/files/13253741/TestSceneDragAndDrop.zip)

editor_selection->add_node(selected);
				EditorNode::get_singleton()->edit_node(selected);
			}
		}
		if (editor_selection->get_selected_node_list().size() == 1) {
			EditorNode::get_singleton()->edit_node(editor_selection->get_selected_node_list()[0]);
		}
	}
}
ObjectID Node3DEditorViewport::_select_ray(const Point2 &p_pos) const {
	Vector3 ray = _get_ray(p_pos);
	Vector3 pos = _get_ray_pos(p_pos);
	Vector2 shrinked_pos = p_pos / subviewport_container->get_stretch_shrink();
	if (viewport->get_debug_draw() == Viewport::DEBUG_DRAW_SDFGI_PROBES) {
		RS::get_singleton()->sdfgi_set_debug_probe_select(pos, ray);
	}
	Vector<ObjectID> instances = RenderingServer::get_singleton()->instances_cull_ray(pos, pos + ray * camera->get_far(), get_tree()->get_root()->get_world_3d()->get_scenario());
	HashSet<Ref<EditorNode3DGizmo>> found_gizmos;
	Node *edited_scene = get_tree()->get_edited_scene_root();
	ObjectID closest;
	Node *item = nullptr;
	float closest_dist = 1e20;
	for (int i = 0; i < instances.size(); i++) {
		Node3D *spat = Object::cast_to<Node3D>(ObjectDB::get_instance(instances[i]));
		if (!spat) {
			continue;
		}
		Vector<Ref<Node3DGizmo>> gizmos = spat->get_gizmos();
		for (int j = 0; j < gizmos.size(); j++) {
			Ref<EditorNode3DGizmo> seg = gizmos[j];