### 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)

ClassDB::bind_method(D_METHOD("_update_type_items"), &ThemeTypeEditor::_update_type_items);
	ClassDB::bind_method(D_METHOD("_pin_leading_stylebox"), &ThemeTypeEditor::_pin_leading_stylebox);
	ClassDB::bind_method(D_METHOD("_unpin_leading_stylebox"), &ThemeTypeEditor::_unpin_leading_stylebox);
	ClassDB::bind_method(D_METHOD("_change_pinned_stylebox"), &ThemeTypeEditor::_change_pinned_stylebox);
}
void ThemeTypeEditor::set_edited_theme(const Ref<Theme> &p_theme) {
	if (edited_theme.is_valid()) {
		edited_theme->disconnect("changed", callable_mp(this, &ThemeTypeEditor::_update_type_list_debounced));
	}
	edited_theme = p_theme;
	if (edited_theme.is_valid()) {
		edited_theme->connect("changed", callable_mp(this, &ThemeTypeEditor::_update_type_list_debounced));
		_update_type_list();
	}
	add_type_dialog->set_edited_theme(edited_theme);
}
void ThemeTypeEditor::select_type(String p_type_name) {