### 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)

}
			return table_offy;
		}
		off.y += TS->shaped_text_get_descent(rid) + theme_cache.line_separation;
	}
	
	if (line_clicked) {
		
		if (r_click_item != nullptr) {
			Item *it = p_frame->lines[p_line].from;
			Item *it_to = (p_line + 1 < (int)p_frame->lines.size()) ? p_frame->lines[p_line + 1].from : nullptr;
			if (char_pos >= 0) {
				*r_click_item = _get_item_at_pos(it, it_to, char_pos);
			} else {
				int stop = text_rect_begin;
				*r_click_item = _find_indentable(it);
				while (*r_click_item) {
					Ref<Font> font = theme_cache.normal_font;
					int font_size = theme_cache.normal_font_size;
					ItemFont *font_it = _find_font(*r_click_item);
					if (font_it) {
						if (font_it->font.is_valid()) {
							font = font_it->font;
						}
						if (font_it->font_size > 0) {
							font_size = font_it->font_size;
						}
					}
					ItemFontSize *font_size_it = _find_font_size(*r_click_item);
					if (font_size_it && font_size_it->font_size > 0) {