### 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)

FontAdvanced *fd = font_owner.get_or_null(p_font_rid);
	ERR_FAIL_COND_V(!fd, Ref<Image>());
	MutexLock lock(fd->mutex);
	Vector2i size = _get_size_outline(fd, p_size);
	ERR_FAIL_COND_V(!_ensure_cache_for_size(fd, size), Ref<Image>());
	ERR_FAIL_INDEX_V(p_texture_index, fd->cache[size]->textures.size(), Ref<Image>());
	const ShelfPackTexture &tex = fd->cache[size]->textures[p_texture_index];
	return Image::create_from_data(tex.texture_w, tex.texture_h, false, tex.format, tex.imgdata);
}
void TextServerAdvanced::_font_set_texture_offsets(const RID &p_font_rid, const Vector2i &p_size, int64_t p_texture_index, const PackedInt32Array &p_offsets) {
	ERR_FAIL_COND(p_offsets.size() % 4 != 0);
	FontAdvanced *fd = font_owner.get_or_null(p_font_rid);
	ERR_FAIL_COND(!fd);
	MutexLock lock(fd->mutex);
	Vector2i size = _get_size_outline(fd, p_size);
	ERR_FAIL_COND(!_ensure_cache_for_size(fd, size));
	ERR_FAIL_COND(p_texture_index < 0);
	if (p_texture_index >= fd->cache[size]->textures.size()) {
		fd->cache[size]->textures.resize(p_texture_index + 1);
	}
	ShelfPackTexture &tex = fd->cache[size]->textures.write[p_texture_index];
	tex.shelves.clear();
	for (int32_t i = 0; i < p_offsets.size(); i += 4) {
		tex.shelves.push_back(Shelf(p_offsets[i], p_offsets[i + 1], p_offsets[i + 2], p_offsets[i + 3]));
	}
}
PackedInt32Array TextServerAdvanced::_font_get_texture_offsets(const RID &p_font_rid, const Vector2i &p_size, int64_t p_texture_index) const {