### 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;
	_internal_set_size(p_size);
}
void SubViewport::set_size_force(const Size2i &p_size) {
	ERR_MAIN_THREAD_GUARD;
	// Use only for setting the size from the parent SubViewportContainer with enabled stretch mode.
	// Don't expose function to scripting.
	_internal_set_size(p_size, true);
}
void SubViewport::_internal_set_size(const Size2i &p_size, bool p_force) {
	SubViewportContainer *c = Object::cast_to<SubViewportContainer>(get_parent());
	if (!p_force && c && c->is_stretch_enabled()) {
#ifdef DEBUG_ENABLED
		WARN_PRINT("Can't change the size of a `SubViewport` with a `SubViewportContainer` parent that has `stretch` enabled. Set `SubViewportContainer.stretch` to `false` to allow changing the size manually.");
#endif // DEBUG_ENABLED
		return;
	}
	_set_size(p_size, _get_size_2d_override(), true);
	if (c) {
		c->update_minimum_size();
	}
}
Size2i SubViewport::get_size() const {