### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Window 11, Forward+, GTX 1060

### Issue description

Adding two theme variations in a row result to a  crash.

https://user-images.githubusercontent.com/93253123/217037249-1ce1d56d-beb6-4435-83ad-9f8a07fe0e96.mp4



### Steps to reproduce

1. Create a project.
2. Create a theme.
3. Double click to go in the theme editor.
4. Click on manage items buttons.
5. In the add type field type a name to add a type.
6. type another name to add a second type.
7. Crash.

### Minimal reproduction project

[ThemeVariationCrash.zip](https://github.com/godotengine/godot/files/10665863/ThemeVariationCrash.zip)

update_debounce_timer->start();
}
HashMap<StringName, bool> ThemeTypeEditor::_get_type_items(String p_type_name, void (Theme::*get_list_func)(StringName, List<StringName> *) const, bool include_default) {
	HashMap<StringName, bool> items;
	List<StringName> names;
	if (include_default) {
		names.clear();