### 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(MSAA_DISABLED);
	return msaa_2d;
}
void Viewport::set_msaa_3d(MSAA p_msaa) {
	ERR_MAIN_THREAD_GUARD;
	ERR_FAIL_INDEX(p_msaa, MSAA_MAX);
	if (msaa_3d == p_msaa) {
		return;
	}
	msaa_3d = p_msaa;
	RS::get_singleton()->viewport_set_msaa_3d(viewport, RS::ViewportMSAA(p_msaa));
}
Viewport::MSAA Viewport::get_msaa_3d() const {
	ERR_READ_THREAD_GUARD_V(MSAA_DISABLED);
	return msaa_3d;
}
void Viewport::set_screen_space_aa(ScreenSpaceAA p_screen_space_aa) {
	ERR_MAIN_THREAD_GUARD;
	ERR_FAIL_INDEX(p_screen_space_aa, SCREEN_SPACE_AA_MAX);
	if (screen_space_aa == p_screen_space_aa) {
		return;
	}
	screen_space_aa = p_screen_space_aa;
	RS::get_singleton()->viewport_set_screen_space_aa(viewport, RS::ViewportScreenSpaceAA(p_screen_space_aa));
}
Viewport::ScreenSpaceAA Viewport::get_screen_space_aa() const {
	ERR_READ_THREAD_GUARD_V(SCREEN_SPACE_AA_DISABLED);
	return screen_space_aa;
}
void Viewport::set_use_taa(bool p_use_taa) {