### 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)

}
		String segment;
		if (list_items[i]->list_type == LIST_DOTS) {
			static const char32_t _prefix[2] = { 0x25CF, 0 };
			prefix = _prefix;
			break;
		} else if (list_items[i]->list_type == LIST_NUMBERS) {
			segment = itos(list_index[i]);
			if (is_localizing_numeral_system()) {
				segment = TS->format_number(segment, _find_language(l.from));
			}
		} else if (list_items[i]->list_type == LIST_LETTERS) {
			segment = _letters(list_index[i], list_items[i]->capitalize);
		} else if (list_items[i]->list_type == LIST_ROMAN) {
			segment = _roman(list_index[i], list_items[i]->capitalize);
		}
		if (rtl) {
			prefix = prefix + segment;
		} else {
			prefix = segment + prefix;
		}
	}
	if (!prefix.is_empty()) {
		Ref<Font> font = theme_cache.normal_font;
		int font_size = theme_cache.normal_font_size;
		ItemFont *font_it = _find_font(l.from);
		if (font_it) {
			if (font_it->font.is_valid()) {
				font = font_it->font;
			}