### 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)

_update_name();
		} break;
		case VIEW_SWITCH_PERSPECTIVE_ORTHOGONAL: {
			_menu_option(orthogonal ? VIEW_PERSPECTIVE : VIEW_ORTHOGONAL);
		} break;
		case VIEW_AUTO_ORTHOGONAL: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_AUTO_ORTHOGONAL);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			current = !current;
			view_menu->get_popup()->set_item_checked(idx, current);
			if (auto_orthogonal) {
				auto_orthogonal = false;
				_update_name();
			}
		} break;
		case VIEW_LOCK_ROTATION: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_LOCK_ROTATION);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			_set_lock_view_rotation(!current);
		} break;
		case VIEW_AUDIO_LISTENER: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_AUDIO_LISTENER);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			current = !current;
			viewport->set_as_audio_listener_3d(current);
			view_menu->get_popup()->set_item_checked(idx, current);
		} break;
		case VIEW_AUDIO_DOPPLER: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_AUDIO_DOPPLER);
			bool current = view_menu->get_popup()->is_item_checked(idx);