### 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)

import_bulk_sc->set_custom_minimum_size(Size2(260.0, 0.0) * EDSCALE);
	import_bulk_sc->set_horizontal_scroll_mode(ScrollContainer::SCROLL_MODE_DISABLED);
	import_main_hb->add_child(import_bulk_sc);
	VBoxContainer *import_bulk_vb = memnew(VBoxContainer);
	import_bulk_vb->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	import_bulk_sc->add_child(import_bulk_vb);
	Label *import_bulk_label = memnew(Label);
	import_bulk_label->set_text(TTR("Select by data type:"));
	import_bulk_vb->add_child(import_bulk_label);
	select_colors_icon = memnew(TextureRect);
	select_colors_label = memnew(Label);
	deselect_all_colors_button = memnew(Button);
	select_all_colors_button = memnew(Button);
	select_full_colors_button = memnew(Button);
	total_selected_colors_label = memnew(Label);
	select_constants_icon = memnew(TextureRect);
	select_constants_label = memnew(Label);
	deselect_all_constants_button = memnew(Button);
	select_all_constants_button = memnew(Button);
	select_full_constants_button = memnew(Button);
	total_selected_constants_label = memnew(Label);
	select_fonts_icon = memnew(TextureRect);
	select_fonts_label = memnew(Label);
	deselect_all_fonts_button = memnew(Button);
	select_all_fonts_button = memnew(Button);
	select_full_fonts_button = memnew(Button);
	total_selected_fonts_label = memnew(Label);
	select_font_sizes_icon = memnew(TextureRect);
	select_font_sizes_label = memnew(Label);
	deselect_all_font_sizes_button = memnew(Button);