### 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)

ERR_FAIL_COND_V(p_size.x <= 0, false);
	if (p_font_data->cache.has(p_size)) {
		return true;
	}
	FontForSizeAdvanced *fd = memnew(FontForSizeAdvanced);
	fd->size = p_size;
	if (p_font_data->data_ptr && (p_font_data->data_size > 0)) {
		
#ifdef MODULE_FREETYPE_ENABLED
		int error = 0;
		if (!ft_library) {
			error = FT_Init_FreeType(&ft_library);
			if (error != 0) {
				memdelete(fd);
				ERR_FAIL_V_MSG(false, "FreeType: Error initializing library: '" + String(FT_Error_String(error)) + "'.");
			}
#ifdef MODULE_SVG_ENABLED
			FT_Property_Set(ft_library, "ot-svg", "svg-hooks", get_tvg_svg_in_ot_hooks());
#endif
		}
		memset(&fd->stream, 0, sizeof(FT_StreamRec));
		fd->stream.base = (unsigned char *)p_font_data->data_ptr;
		fd->stream.size = p_font_data->data_size;
		fd->stream.pos = 0;
		FT_Open_Args fargs;
		memset(&fargs, 0, sizeof(FT_Open_Args));