### 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 "node_3d_editor_plugin.h"
#include "core/config/project_settings.h"
#include "core/input/input.h"
#include "core/input/input_map.h"
#include "core/math/math_funcs.h"
#include "core/math/projection.h"
#include "core/os/keyboard.h"
#include "editor/debugger/editor_debugger_node.h"
#include "editor/editor_node.h"
#include "editor/editor_settings.h"
#include "editor/editor_string_names.h"
#include "editor/editor_undo_redo_manager.h"
#include "editor/gui/editor_run_bar.h"
#include "editor/gui/editor_spin_slider.h"
#include "editor/plugins/animation_player_editor_plugin.h"
#include "editor/plugins/gizmos/audio_listener_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/audio_stream_player_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/camera_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/collision_object_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/collision_polygon_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/collision_shape_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/cpu_particles_3d_gizmo_plugin.h"
#include "editor/plugins/gizmos/decal_gizmo_plugin.h"
#include "editor/plugins/gizmos/fog_volume_gizmo_plugin.h"
#include "editor/plugins/gizmos/gpu_particles_3d_gizmo_plugin.h"