### 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)

GDCLASS(SubViewport, Viewport);
public:
	enum ClearMode {
		CLEAR_MODE_ALWAYS,
		CLEAR_MODE_NEVER,
		CLEAR_MODE_ONCE
	};
	enum UpdateMode {
		UPDATE_DISABLED,
		UPDATE_ONCE, 
		UPDATE_WHEN_VISIBLE, 
		UPDATE_WHEN_PARENT_VISIBLE,
		UPDATE_ALWAYS
	};
private:
	UpdateMode update_mode = UPDATE_WHEN_VISIBLE;
	ClearMode clear_mode = CLEAR_MODE_ALWAYS;
	bool size_2d_override_stretch = false;
	void _internal_set_size(const Size2i &p_size, bool p_force = false);
protected:
	static void _bind_methods();
	virtual DisplayServer::WindowID get_window_id() const override;
	void _notification(int p_what);
public:
	void set_size(const Size2i &p_size);
	Size2i get_size() const;
	void set_size_force(const Size2i &p_size);
	void set_size_2d_override(const Size2i &p_size);
	Size2i get_size_2d_override() const;
	void set_size_2d_override_stretch(bool p_enable);