### 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_READ_THREAD_GUARD_V(Transform2D());
	return canvas_transform;
}
void Viewport::_update_global_transform() {
	Transform2D sxform = stretch_transform * global_canvas_transform;
	RenderingServer::get_singleton()->viewport_set_global_canvas_transform(viewport, sxform);
}
void Viewport::set_global_canvas_transform(const Transform2D &p_transform) {
	ERR_MAIN_THREAD_GUARD;
	global_canvas_transform = p_transform;
	_update_global_transform();
}
Transform2D Viewport::get_global_canvas_transform() const {
	ERR_READ_THREAD_GUARD_V(Transform2D());
	return global_canvas_transform;
}
void Viewport::_camera_2d_set(Camera2D *p_camera_2d) {
	camera_2d = p_camera_2d;
}
void Viewport::_audio_listener_2d_set(AudioListener2D *p_listener) {
	if (audio_listener_2d == p_listener) {
		return;
	} else if (audio_listener_2d) {
		audio_listener_2d->clear_current();
	}
	audio_listener_2d = p_listener;
}
void Viewport::_audio_listener_2d_remove(AudioListener2D *p_listener) {