### 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_READ_THREAD_GUARD_V(false);
	return use_xr;
}
void Viewport::set_scaling_3d_mode(Scaling3DMode p_scaling_3d_mode) {
	ERR_MAIN_THREAD_GUARD;
	if (scaling_3d_mode == p_scaling_3d_mode) {
		return;
	}
	scaling_3d_mode = p_scaling_3d_mode;
	RS::get_singleton()->viewport_set_scaling_3d_mode(viewport, (RS::ViewportScaling3DMode)(int)p_scaling_3d_mode);
}
Viewport::Scaling3DMode Viewport::get_scaling_3d_mode() const {
	ERR_READ_THREAD_GUARD_V(SCALING_3D_MODE_BILINEAR);
	return scaling_3d_mode;
}
void Viewport::set_scaling_3d_scale(float p_scaling_3d_scale) {