### 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)

void clear();
	void set_offset(int p_pixel);
	void set_meta_underline(bool p_underline);
	bool is_meta_underlined() const;
	void set_hint_underline(bool p_underline);
	bool is_hint_underlined() const;
	void set_override_selected_font_color(bool p_override_selected_font_color);
	bool is_overriding_selected_font_color() const;
	void set_scroll_active(bool p_active);
	bool is_scroll_active() const;
	void set_scroll_follow(bool p_follow);
	bool is_scroll_following() const;
	void set_tab_size(int p_spaces);
	int get_tab_size() const;
	void set_context_menu_enabled(bool p_enabled);
	bool is_context_menu_enabled() const;
	void set_shortcut_keys_enabled(bool p_enabled);
	bool is_shortcut_keys_enabled() const;
	void set_fit_content(bool p_enabled);
	bool is_fit_content_enabled() const;
	bool search(const String &p_string, bool p_from_selection = false, bool p_search_previous = false);
	void scroll_to_paragraph(int p_paragraph);
	int get_paragraph_count() const;
	int get_visible_paragraph_count() const;
	float get_line_offset(int p_line);
	float get_paragraph_offset(int p_paragraph);
	void scroll_to_line(int p_line);
	int get_line_count() const;
	int get_visible_line_count() const;
	int get_content_height() const;