### 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)

display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("VoxelGI Lighting"), VIEW_DISPLAY_DEBUG_VOXEL_GI_LIGHTING);
	display_submenu->add_radio_check_item(TTR("VoxelGI Albedo"), VIEW_DISPLAY_DEBUG_VOXEL_GI_ALBEDO);
	display_submenu->add_radio_check_item(TTR("VoxelGI Emission"), VIEW_DISPLAY_DEBUG_VOXEL_GI_EMISSION);
	display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("SDFGI Cascades"), VIEW_DISPLAY_DEBUG_SDFGI);
	display_submenu->add_radio_check_item(TTR("SDFGI Probes"), VIEW_DISPLAY_DEBUG_SDFGI_PROBES);
	display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("Scene Luminance"), VIEW_DISPLAY_DEBUG_SCENE_LUMINANCE);
	display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("SSAO"), VIEW_DISPLAY_DEBUG_SSAO);
	display_submenu->add_radio_check_item(TTR("SSIL"), VIEW_DISPLAY_DEBUG_SSIL);
	display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("VoxelGI/SDFGI Buffer"), VIEW_DISPLAY_DEBUG_GI_BUFFER);
	display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("Disable Mesh LOD"), VIEW_DISPLAY_DEBUG_DISABLE_LOD);
	display_submenu->add_separator();
	display_submenu->add_radio_check_item(TTR("OmniLight3D Cluster"), VIEW_DISPLAY_DEBUG_CLUSTER_OMNI_LIGHTS);
	display_submenu->add_radio_check_item(TTR("SpotLight3D Cluster"), VIEW_DISPLAY_DEBUG_CLUSTER_SPOT_LIGHTS);
	display_submenu->add_radio_check_item(TTR("Decal Cluster"), VIEW_DISPLAY_DEBUG_CLUSTER_DECALS);
	display_submenu->add_radio_check_item(TTR("ReflectionProbe Cluster"), VIEW_DISPLAY_DEBUG_CLUSTER_REFLECTION_PROBES);
	display_submenu->add_radio_check_item(TTR("Occlusion Culling Buffer"), VIEW_DISPLAY_DEBUG_OCCLUDERS);
	display_submenu->add_radio_check_item(TTR("Motion Vectors"), VIEW_DISPLAY_MOTION_VECTORS);
	display_submenu->add_radio_check_item(TTR("Internal Buffer"), VIEW_DISPLAY_INTERNAL_BUFFER);
	display_submenu->set_name("DisplayAdvanced");
	view_menu->get_popup()->add_submenu_item(TTR("Display Advanced..."), "DisplayAdvanced", VIEW_DISPLAY_ADVANCED);
	view_menu->get_popup()->add_separator();
	view_menu->get_popup()->add_check_shortcut(ED_SHORTCUT("spatial_editor/view_environment", TTR("View Environment")), VIEW_ENVIRONMENT);
	view_menu->get_popup()->add_check_shortcut(ED_SHORTCUT("spatial_editor/view_gizmos", TTR("View Gizmos")), VIEW_GIZMOS);
	view_menu->get_popup()->add_check_shortcut(ED_SHORTCUT("spatial_editor/view_information", TTR("View Information")), VIEW_INFORMATION);