### 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, PackedInt32Array());
	MutexLock lock(fd->mutex);
	Vector2i size = _get_size_outline(fd, p_size);
	ERR_FAIL_COND_V(!_ensure_cache_for_size(fd, size), PackedInt32Array());
	ERR_FAIL_INDEX_V(p_texture_index, fd->cache[size]->textures.size(), PackedInt32Array());
	const ShelfPackTexture &tex = fd->cache[size]->textures[p_texture_index];
	PackedInt32Array ret;
	ret.resize(tex.shelves.size() * 4);
	int32_t *wr = ret.ptrw();
	int32_t i = 0;
	for (const Shelf &E : tex.shelves) {
		wr[i * 4] = E.x;
		wr[i * 4 + 1] = E.y;
		wr[i * 4 + 2] = E.w;
		wr[i * 4 + 3] = E.h;
		i++;
	}
	return ret;
}
PackedInt32Array TextServerAdvanced::_font_get_glyph_list(const RID &p_font_rid, const Vector2i &p_size) const {