### 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)

case VIEW_HALF_RESOLUTION: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_HALF_RESOLUTION);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			view_menu->get_popup()->set_item_checked(idx, !current);
			_update_shrink();
		} break;
		case VIEW_INFORMATION: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_INFORMATION);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			view_menu->get_popup()->set_item_checked(idx, !current);
		} break;
		case VIEW_FRAME_TIME: {
			int idx = view_menu->get_popup()->get_item_index(VIEW_FRAME_TIME);
			bool current = view_menu->get_popup()->is_item_checked(idx);
			view_menu->get_popup()->set_item_checked(idx, !current);
		} break;
		case VIEW_DISPLAY_NORMAL:
		case VIEW_DISPLAY_WIREFRAME:
		case VIEW_DISPLAY_OVERDRAW:
		case VIEW_DISPLAY_UNSHADED:
		case VIEW_DISPLAY_LIGHTING:
		case VIEW_DISPLAY_NORMAL_BUFFER:
		case VIEW_DISPLAY_DEBUG_SHADOW_ATLAS:
		case VIEW_DISPLAY_DEBUG_DIRECTIONAL_SHADOW_ATLAS:
		case VIEW_DISPLAY_DEBUG_VOXEL_GI_ALBEDO:
		case VIEW_DISPLAY_DEBUG_VOXEL_GI_LIGHTING:
		case VIEW_DISPLAY_DEBUG_VOXEL_GI_EMISSION:
		case VIEW_DISPLAY_DEBUG_SCENE_LUMINANCE:
		case VIEW_DISPLAY_DEBUG_SSAO:
		case VIEW_DISPLAY_DEBUG_SSIL: