### 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)

void Node3DEditorViewport::set_freelook_active(bool active_now) {
	if (!freelook_active && active_now) {
		
		cursor = camera_cursor;
		
		Vector3 forward = to_camera_transform(cursor).basis.xform(Vector3(0, 0, -1));
		cursor.eye_pos = cursor.pos - cursor.distance * forward;
		
		camera_cursor.eye_pos = cursor.eye_pos;
		if (EDITOR_GET("editors/3d/freelook/freelook_speed_zoom_link")) {
			
			real_t base_speed = EDITOR_GET("editors/3d/freelook/freelook_base_speed");
			freelook_speed = base_speed * cursor.distance;
		}
		previous_mouse_position = get_local_mouse_position();
		
		Input::get_singleton()->set_mouse_mode(Input::MOUSE_MODE_CAPTURED);
	} else if (freelook_active && !active_now) {
		
		cursor = camera_cursor;
		
		Input::get_singleton()->set_mouse_mode(Input::MOUSE_MODE_VISIBLE);
		
		
		
		warp_mouse(previous_mouse_position);
	}
	freelook_active = active_now;
}
void Node3DEditorViewport::scale_fov(real_t p_fov_offset) {