### 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)

}
			changing++;
			if (update_tree_pending) {
				update_tree();
				update_tree_pending = false;
				pending.clear();
			} else {
				while (pending.size()) {
					StringName prop = *pending.begin();
					if (editor_property_map.has(prop)) {
						for (EditorProperty *E : editor_property_map[prop]) {
							E->update_property();
							E->update_editor_property_status();
							E->update_cache();
						}
					}
					pending.remove(pending.begin());
				}
			}
			changing--;
		} break;
		case EditorSettings::NOTIFICATION_EDITOR_SETTINGS_CHANGED: {
			_update_inspector_bg();
			if (EditorSettings::get_singleton()->check_changed_settings_in_group("interface/inspector")) {
				update_tree();
			}
		} break;
	}
}
void EditorInspector::_changed_callback() {