### 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_DISPLAY_DEBUG_PSSM_SPLITS:
		case VIEW_DISPLAY_DEBUG_DECAL_ATLAS:
		case VIEW_DISPLAY_DEBUG_SDFGI:
		case VIEW_DISPLAY_DEBUG_SDFGI_PROBES:
		case VIEW_DISPLAY_DEBUG_GI_BUFFER:
		case VIEW_DISPLAY_DEBUG_DISABLE_LOD:
		case VIEW_DISPLAY_DEBUG_CLUSTER_OMNI_LIGHTS:
		case VIEW_DISPLAY_DEBUG_CLUSTER_SPOT_LIGHTS:
		case VIEW_DISPLAY_DEBUG_CLUSTER_DECALS:
		case VIEW_DISPLAY_DEBUG_CLUSTER_REFLECTION_PROBES:
		case VIEW_DISPLAY_DEBUG_OCCLUDERS:
		case VIEW_DISPLAY_MOTION_VECTORS:
		case VIEW_DISPLAY_INTERNAL_BUFFER: {
			static const int display_options[] = {
				VIEW_DISPLAY_NORMAL,
				VIEW_DISPLAY_WIREFRAME,
				VIEW_DISPLAY_OVERDRAW,
				VIEW_DISPLAY_UNSHADED,
				VIEW_DISPLAY_LIGHTING,
				VIEW_DISPLAY_NORMAL_BUFFER,
				VIEW_DISPLAY_DEBUG_SHADOW_ATLAS,
				VIEW_DISPLAY_DEBUG_DIRECTIONAL_SHADOW_ATLAS,
				VIEW_DISPLAY_DEBUG_VOXEL_GI_ALBEDO,
				VIEW_DISPLAY_DEBUG_VOXEL_GI_LIGHTING,
				VIEW_DISPLAY_DEBUG_VOXEL_GI_EMISSION,
				VIEW_DISPLAY_DEBUG_SCENE_LUMINANCE,
				VIEW_DISPLAY_DEBUG_SSAO,
				VIEW_DISPLAY_DEBUG_SSIL,
				VIEW_DISPLAY_DEBUG_GI_BUFFER,
				VIEW_DISPLAY_DEBUG_DISABLE_LOD,