### 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)

}
	} else if (selected_nodes.size() == 0) {
		if (root_node) {
			target_node = root_node;
		} else {
			/
			SceneTreeDock::get_singleton()->add_root_node(memnew(Node3D));
			target_node = get_tree()->get_edited_scene_root();
		}
	} else {
		accept->set_text(TTR("Cannot drag and drop into multiple selected nodes."));
		accept->popup_centered();
		_remove_preview_node();
		return;
	}
	drop_pos = p_point;
	_perform_drop_data();
}
void Node3DEditorViewport::begin_transform(TransformMode p_mode, bool instant) {
	if (get_selected_count() > 0) {
		_edit.mode = p_mode;
		_compute_edit(_edit.mouse_pos);
		_edit.instant = instant;
		_edit.snap = spatial_editor->is_snap_enabled();
		update_transform_gizmo_view();
		set_process_input(instant);
	}
}
/
void Node3DEditorViewport::commit_transform() {