### 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;
	if (use_taa == p_use_taa) {
		return;
	}
	use_taa = p_use_taa;
	RS::get_singleton()->viewport_set_use_taa(viewport, p_use_taa);
}
bool Viewport::is_using_taa() const {
	ERR_READ_THREAD_GUARD_V(false);
	return use_taa;
}
void Viewport::set_use_debanding(bool p_use_debanding) {
	ERR_MAIN_THREAD_GUARD;
	if (use_debanding == p_use_debanding) {
		return;
	}
	use_debanding = p_use_debanding;
	RS::get_singleton()->viewport_set_use_debanding(viewport, p_use_debanding);
}
bool Viewport::is_using_debanding() const {
	ERR_READ_THREAD_GUARD_V(false);
	return use_debanding;
}
void Viewport::set_mesh_lod_threshold(float p_pixels) {
	ERR_MAIN_THREAD_GUARD;
	mesh_lod_threshold = p_pixels;
	RS::get_singleton()->viewport_set_mesh_lod_threshold(viewport, mesh_lod_threshold);
}
float Viewport::get_mesh_lod_threshold() const {