### Godot version

4.2 eca6f0e

### System information

Windows 10 x64

### Issue description


https://github.com/godotengine/godot/assets/2223172/a2796263-4e2e-4b14-a080-b3ad034cc141



### Steps to reproduce

1. Add SubViewport
2. Add Sprite2D
3. Set spirte's texture to ViewportTexture
4. Create new scene
5. Instance the new scene inside the scene with viewport
6. Make sure both scenes are opened
7. Go to instance scene and save it
8. Go to viewport scene

You will see error spam. Reloading the scene fixes it.

### Minimal reproduction project

[vip.zip](https://github.com/godotengine/godot/files/12292386/vip.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);