### 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;
	
	
	
	scaling_3d_scale = CLAMP(p_scaling_3d_scale, 0.1, 2.0);
	RS::get_singleton()->viewport_set_scaling_3d_scale(viewport, scaling_3d_scale);
}
float Viewport::get_scaling_3d_scale() const {
	ERR_READ_THREAD_GUARD_V(0);
	return scaling_3d_scale;
}
void Viewport::set_fsr_sharpness(float p_fsr_sharpness) {
	ERR_MAIN_THREAD_GUARD;
	if (fsr_sharpness == p_fsr_sharpness) {
		return;
	}
	if (p_fsr_sharpness < 0.0f) {
		p_fsr_sharpness = 0.0f;
	}
	fsr_sharpness = p_fsr_sharpness;
	RS::get_singleton()->viewport_set_fsr_sharpness(viewport, p_fsr_sharpness);
}
float Viewport::get_fsr_sharpness() const {
	ERR_READ_THREAD_GUARD_V(0);
	return fsr_sharpness;
}
void Viewport::set_texture_mipmap_bias(float p_texture_mipmap_bias) {