### 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)

Node3D *sp = Object::cast_to<Node3D>(E.key);
				if (!sp) {
					continue;
				}
				Node3DEditorSelectedItem *se = editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(sp);
				if (!se) {
					continue;
				}
				Transform3D t = sp->get_global_gizmo_transform();
				VisualInstance3D *vi = Object::cast_to<VisualInstance3D>(sp);
				AABB new_aabb = vi ? vi->get_aabb() : _calculate_spatial_bounds(sp);
				exist = true;
				if (se->last_xform == t && se->aabb == new_aabb && !se->last_xform_dirty) {
					continue;
				}
				changed = true;
				se->last_xform_dirty = false;
				se->last_xform = t;
				se->aabb = new_aabb;
				Transform3D t_offset = t;
				
				{
					const Vector3 offset(0.005, 0.005, 0.005);
					Basis aabb_s;
					aabb_s.scale(se->aabb.size + offset);
					t.translate_local(se->aabb.position - offset / 2);
					t.basis = t.basis * aabb_s;
				}
				{
					const Vector3 offset(0.01, 0.01, 0.01);