### 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)

constant_amount += filtered_names.size();
					break;
				case Theme::DATA_TYPE_FONT:
					data_type_node->set_icon(0, get_theme_icon(SNAME("Font"), SNAME("EditorIcons")));
					data_type_node->set_text(0, TTR("Fonts"));
					item_list = &tree_font_items;
					font_amount += filtered_names.size();
					break;
				case Theme::DATA_TYPE_FONT_SIZE:
					data_type_node->set_icon(0, get_theme_icon(SNAME("FontSize"), SNAME("EditorIcons")));
					data_type_node->set_text(0, TTR("Font Sizes"));
					item_list = &tree_font_size_items;
					font_size_amount += filtered_names.size();
					break;
				case Theme::DATA_TYPE_ICON:
					data_type_node->set_icon(0, get_theme_icon(SNAME("ImageTexture"), SNAME("EditorIcons")));
					data_type_node->set_text(0, TTR("Icons"));
					item_list = &tree_icon_items;
					icon_amount += filtered_names.size();
					break;
				case Theme::DATA_TYPE_STYLEBOX:
					data_type_node->set_icon(0, get_theme_icon(SNAME("StyleBoxFlat"), SNAME("EditorIcons")));
					data_type_node->set_text(0, TTR("Styleboxes"));
					item_list = &tree_stylebox_items;
					stylebox_amount += filtered_names.size();
					break;
				case Theme::DATA_TYPE_MAX:
					break; 
			}
			filtered_names.sort_custom<StringName::AlphCompare>();