### 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)

}
			undo_redo->commit_action();
		} break;
		case VIEW_ENVIRONMENT: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_ENVIRONMENT);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			current = !current;
			if (current) {
				camera->set_environment(Ref<Resource>());
			} else {
				camera->set_environment(Node3DEditor::get_singleton()->get_viewport_environment());
			}
			view_menu->get_popup()->set_item_checked(idx, current);
		} break;
		case VIEW_PERSPECTIVE: {
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(VIEW_PERSPECTIVE), true);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(VIEW_ORTHOGONAL), false);
			orthogonal = false;
			auto_orthogonal = false;
			call_deferred(SNAME("update_transform_gizmo_view"));
			_update_camera(0);
			_update_name();
		} break;
		case VIEW_ORTHOGONAL: {
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(VIEW_PERSPECTIVE), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(VIEW_ORTHOGONAL), true);
			orthogonal = true;
			auto_orthogonal = false;
			call_deferred(SNAME("update_transform_gizmo_view"));
			_update_camera(0);