### 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)

String get_selected_path() const;
	void update_tree();
	void update_property(const String &p_prop);
	void edit(Object *p_object);
	Object *get_edited_object();
	void set_keying(bool p_active);
	void set_read_only(bool p_read_only);
	EditorPropertyNameProcessor::Style get_property_name_style() const;
	void set_property_name_style(EditorPropertyNameProcessor::Style p_style);
	void set_autoclear(bool p_enable);
	void set_show_categories(bool p_show);
	void set_use_doc_hints(bool p_enable);
	void set_hide_script(bool p_hide);
	void set_hide_metadata(bool p_hide);
	void set_use_filter(bool p_use);
	void register_text_enter(Node *p_line_edit);
	void set_use_folding(bool p_enable);
	bool is_using_folding();
	void collapse_all_folding();
	void expand_all_folding();
	void expand_revertable();
	void set_scroll_offset(int p_offset);
	int get_scroll_offset() const;
	void set_property_prefix(const String &p_prefix);
	String get_property_prefix() const;
	void set_object_class(const String &p_class);
	String get_object_class() const;
	void set_use_wide_editors(bool p_enable);
	void set_sub_inspector(bool p_enable);
	bool is_sub_inspector() const { return sub_inspector; }