### 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)

GDCLASS(EditorInspectorSection, Container);
	String label;
	String section;
	bool vbox_added = false; 
	Color bg_color;
	bool foldable = false;
	int indent_depth = 0;
	Timer *dropping_unfold_timer = nullptr;
	bool dropping = false;
	bool dropping_for_unfold = false;
	HashSet<StringName> revertable_properties;
	void _test_unfold();
	int _get_header_height();
	Ref<Texture2D> _get_arrow();
protected:
	Object *object = nullptr;
	VBoxContainer *vbox = nullptr;
	void _notification(int p_what);
	static void _bind_methods();
	virtual void gui_input(const Ref<InputEvent> &p_event) override;
public:
	virtual Size2 get_minimum_size() const override;
	void setup(const String &p_section, const String &p_label, Object *p_object, const Color &p_bg_color, bool p_foldable, int p_indent_depth = 0);
	VBoxContainer *get_vbox();
	void unfold();
	void fold();
	bool has_revertable_properties() const;
	void property_can_revert_changed(const String &p_path, bool p_can_revert);