### 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)

int original_focus = focused_axis;
	focused_axis = -2;
	Vector2 mouse_pos = get_local_mouse_position();
	if (mouse_pos.distance_to(get_size() / 2.0) < get_size().x / 2.0) {
		focused_axis = -1;
	}
	Vector<Axis2D> axes;
	_get_sorted_axis(axes);
	for (int i = 0; i < axes.size(); i++) {
		const Axis2D &axis = axes[i];
		if (mouse_pos.distance_to(axis.screen_point) < AXIS_CIRCLE_RADIUS) {
			focused_axis = axis.axis;
		}
	}
	if (focused_axis != original_focus) {
		queue_redraw();
	}
}
void ViewportRotationControl::_on_mouse_exited() {