### Godot version

v4.0 rc6

### System information

Windows 10

### Issue description

When using a ViewportTexture from a SubViewport on a TextureRect, it throws errors after running the scene once and then switching scenes in the editor.
![Pasted image 20230227212626](https://user-images.githubusercontent.com/44676282/221680047-984fa03e-33d1-4856-9a7f-1700b28423cf.png)


### Steps to reproduce

Run the canvas-scene once.
Switch to another scene in the editor.
Switch back to the canvas-scene

### Minimal reproduction project

[ViewportTextureError.zip](https://github.com/godotengine/godot/files/10844099/ViewportTextureError.zip)

ERR_MAIN_THREAD_GUARD;
	Transform2D xform = get_screen_transform_internal();
	Vector2 gpos = xform.xform(p_position);
	Input::get_singleton()->warp_mouse(gpos);
}
void Viewport::_gui_sort_roots() {
	if (!gui.roots_order_dirty) {
		return;
	}
	gui.roots.sort_custom<Control::CComparator>();
	gui.roots_order_dirty = false;
}
void Viewport::_gui_cancel_tooltip() {
	gui.tooltip_control = nullptr;
	if (gui.tooltip_timer.is_valid()) {
		gui.tooltip_timer->release_connections();
		gui.tooltip_timer = Ref<SceneTreeTimer>();
	}
	if (gui.tooltip_popup) {
		gui.tooltip_popup->queue_free();
	}
}
String Viewport::_gui_get_tooltip(Control *p_control, const Vector2 &p_pos, Control **r_tooltip_owner) {