### 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 oversampling;
}
void TextServerAdvanced::_font_set_global_oversampling(double p_oversampling) {
	_THREAD_SAFE_METHOD_
	if (oversampling != p_oversampling) {
		oversampling = p_oversampling;
		List<RID> fonts;
		font_owner.get_owned_list(&fonts);
		bool font_cleared = false;
		for (const RID &E : fonts) {
			if (!_font_is_multichannel_signed_distance_field(E) && _font_get_oversampling(E) <= 0) {
				_font_clear_size_cache(E);
				font_cleared = true;
			}
		}
		if (font_cleared) {
			List<RID> text_bufs;
			shaped_owner.get_owned_list(&text_bufs);
			for (const RID &E : text_bufs) {
				invalidate(shaped_owner.get_or_null(E), false);
			}
		}
	}
}
int64_t TextServerAdvanced::_convert_pos(const String &p_utf32, const Char16String &p_utf16, int64_t p_pos) const {