### 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)

}
					surface->queue_redraw();
				}
			} break;
			default:
				break;
		}
	}
	Ref<InputEventMouseMotion> m = p_event;
	
	if (m.is_valid() && !_edit.instant) {
		_edit.mouse_pos = m->get_position();
		if (spatial_editor->get_single_selected_node()) {
			Vector<Ref<Node3DGizmo>> gizmos = spatial_editor->get_single_selected_node()->get_gizmos();
			Ref<EditorNode3DGizmo> found_gizmo;
			int found_handle = -1;
			bool found_handle_secondary = false;
			for (int i = 0; i < gizmos.size(); i++) {
				Ref<EditorNode3DGizmo> seg = gizmos[i];
				if (!seg.is_valid()) {
					continue;
				}
				seg->handles_intersect_ray(camera, _edit.mouse_pos, false, found_handle, found_handle_secondary);
				if (found_handle != -1) {
					found_gizmo = seg;
					break;
				}
			}
			if (found_gizmo.is_valid()) {
				spatial_editor->select_gizmo_highlight_axis(-1);