### Godot version

v4.0.beta16.official [518b9e580]

### System information

Windows 10

### Issue description

`RichTextLabel` with `threaded` enabled may crash the game or show the following warning if the node is in another scene:

```
W 0:00:03:0802   test.gd:12 @ load_with_scene(): A Thread object has been re-started without wait_to_finish() having been called on it. Please do so to ensure correct cleanup of the thread.
  <C++ Source>   core/os/thread.cpp:76 @ start()
  <Stack Trace>  test.gd:12 @ load_with_scene()
                 test.gd:6 @ load_items()
                 test.gd:26 @ _on_button_pressed()
```

It may crash the game (without any warning) if it's added directly.

In `v4.0.beta15.official [4fa6edc88]` I was able to reproduce the same warning on my project but I can't reproduce it in the attached MRP. I get a different error and will crash too if the node is added directly:

```
E 0:00:03:0019   remove_from_group: Condition "!E" is true.
  <C++ Source>   scene/main/scene_tree.cpp:157 @ remove_from_group()
```


### Steps to reproduce

Click on the  `Load with scene` or `Load with node` buttons in the attached MRP until it shows a warning/error or crashes. It may take a while.

### Minimal reproduction project

[add_chid_bug_b16.zip](https://github.com/godotengine/godot/files/10521402/add_chid_bug_b16.zip)

int get_content_width() const;
	void scroll_to_selection();
	VScrollBar *get_v_scroll_bar() { return vscroll; }
	virtual CursorShape get_cursor_shape(const Point2 &p_pos) const override;
	virtual Variant get_drag_data(const Point2 &p_point) override;
	void set_selection_enabled(bool p_enabled);
	bool is_selection_enabled() const;
	int get_selection_from() const;
	int get_selection_to() const;
	String get_selected_text() const;
	void select_all();
	void selection_copy();
	void set_deselect_on_focus_loss_enabled(const bool p_enabled);
	bool is_deselect_on_focus_loss_enabled() const;
	void deselect();
	bool is_ready() const;
	void set_threaded(bool p_threaded);
	bool is_threaded() const;
	void set_progress_bar_delay(int p_delay_ms);
	int get_progress_bar_delay() const;
	
	PopupMenu *get_menu() const;
	bool is_menu_visible() const;
	void parse_bbcode(const String &p_bbcode);
	void append_text(const String &p_bbcode);
	void set_use_bbcode(bool p_enable);
	bool is_using_bbcode() const;
	void set_text(const String &p_bbcode);
	String get_text() const;
	void set_text_direction(TextDirection p_text_direction);