### 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)

EditorUndoRedoManager *undo_redo = EditorUndoRedoManager::get_singleton();
	if (spatial_editor->get_preview_material_target().is_valid()) {
		GeometryInstance3D *geometry_instance = Object::cast_to<GeometryInstance3D>(ObjectDB::get_instance(spatial_editor->get_preview_material_target()));
		MeshInstance3D *mesh_instance = Object::cast_to<MeshInstance3D>(ObjectDB::get_instance(spatial_editor->get_preview_material_target()));
		if (mesh_instance && spatial_editor->get_preview_material_surface() != -1) {
			undo_redo->create_action(vformat(TTR("Set Surface %d Override Material"), spatial_editor->get_preview_material_surface()));
			undo_redo->add_do_method(geometry_instance, "set_surface_override_material", spatial_editor->get_preview_material_surface(), spatial_editor->get_preview_material());
			undo_redo->add_undo_method(geometry_instance, "set_surface_override_material", spatial_editor->get_preview_material_surface(), spatial_editor->get_preview_reset_material());
			undo_redo->commit_action();
		} else if (geometry_instance) {
			undo_redo->create_action(TTR("Set Material Override"));
			undo_redo->add_do_method(geometry_instance, "set_material_override", spatial_editor->get_preview_material());
			undo_redo->add_undo_method(geometry_instance, "set_material_override", spatial_editor->get_preview_reset_material());
			undo_redo->commit_action();
		}
		_remove_preview_material();
		return;
	}