### 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)

real_t speed_multiplier = MIN(delta.length() / (get_size().x), 3.0);
			real_t speed = viewport->freelook_speed * speed_multiplier;
			viewport->_nav_pan(nullptr, -delta_normalized * speed);
		} break;
		case Node3DEditorViewport::NAVIGATION_ZOOM: {
			real_t speed_multiplier = MIN(delta.length() / (get_size().x), 3.0);
			real_t speed = viewport->freelook_speed * speed_multiplier;
			viewport->_nav_zoom(nullptr, delta_normalized * speed);
		} break;
		case Node3DEditorViewport::NAVIGATION_ORBIT: {
			real_t speed_multiplier = MIN(delta.length() / (get_size().x), 3.0);
			real_t speed = viewport->freelook_speed * speed_multiplier;
			viewport->_nav_orbit(nullptr, delta_normalized * speed);
		} break;
		case Node3DEditorViewport::NAVIGATION_NONE: {
		} break;
	}
}
void ViewportNavigationControl::_on_mouse_entered() {
	hovered = true;
	queue_redraw();
}
void ViewportNavigationControl::_on_mouse_exited() {
	hovered = false;
	queue_redraw();
}
void ViewportNavigationControl::set_navigation_mode(Node3DEditorViewport::NavigationMode p_nav_mode) {
	nav_mode = p_nav_mode;
}
void ViewportNavigationControl::set_viewport(Node3DEditorViewport *p_viewport) {