### 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)

#include "editor/plugins/gizmos/gpu_particles_collision_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/joint_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/label_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/light_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/lightmap_gi_gizmo_plugin.h"
#include "editor/plugins/gizmos/lightmap_probe_gizmo_plugin.h"
#include "editor/plugins/gizmos/marker_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/mesh_instance_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/navigation_link_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/navigation_region_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/occluder_instance_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/physics_bone_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/ray_cast_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/reflection_probe_gizmo_plugin.h"
#include "editor/plugins/gizmos/shape_cast_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/soft_body_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/spring_arm_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/sprite_base_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/vehicle_body_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/visible_on_screen_notifier_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/voxel_gi_gizmo_plugin.h"
#include "editor/plugins/node_3d_editor_gizmos.h"
#include "editor/scene_tree_dock.h"
#include "scene/3d/camera_3d.h"
#include "scene/3d/collision_shape_3d.h"
#include "scene/3d/decal.h"
#include "scene/3d/light_3d.h"
#include "scene/3d/mesh_instance_3d.h"
#include "scene/3d/physics_body_3d.h"
#include "scene/3d/visual_instance_3d.h"