### 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)

var.tag = amaster->axis[i].tag;
				var.value = (double)amaster->axis[i].def / 65536.0;
				coords.write[i] = amaster->axis[i].def;
				if (p_font_data->variation_coordinates.has(var.tag)) {
					var.value = p_font_data->variation_coordinates[var.tag];
					coords.write[i] = CLAMP(var.value * 65536.0, amaster->axis[i].minimum, amaster->axis[i].maximum);
				}
				if (p_font_data->variation_coordinates.has(_tag_to_name(var.tag))) {
					var.value = p_font_data->variation_coordinates[_tag_to_name(var.tag)];
					coords.write[i] = CLAMP(var.value * 65536.0, amaster->axis[i].minimum, amaster->axis[i].maximum);
				}
				hb_vars.push_back(var);
			}
			FT_Set_Var_Design_Coordinates(fd->face, coords.size(), coords.ptrw());
			hb_font_set_variations(fd->hb_handle, hb_vars.is_empty() ? nullptr : &hb_vars[0], hb_vars.size());
			FT_Done_MM_Var(ft_library, amaster);
		}
#else
		memdelete(fd);
		ERR_FAIL_V_MSG(false, "FreeType: Can't load dynamic font, engine is compiled without FreeType support!");
#endif
	} else {
		
		fd->hb_handle = _bmp_font_create(fd, nullptr);
	}
	p_font_data->cache[p_size] = fd;
	return true;
}
_FORCE_INLINE_ void TextServerAdvanced::_font_clear_cache(FontAdvanced *p_font_data) {