### 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)

}
#endif
	if (!_ensure_glyph(fd, size, index)) {
		return; 
	}
	const FontGlyph &gl = fd->cache[size]->glyph_map[index];
	if (gl.found) {
		ERR_FAIL_COND(gl.texture_idx < -1 || gl.texture_idx >= fd->cache[size]->textures.size());
		if (gl.texture_idx != -1) {
			Color modulate = p_color;
#ifdef MODULE_FREETYPE_ENABLED
			if (fd->cache[size]->face && (fd->cache[size]->textures[gl.texture_idx].format == Image::FORMAT_RGBA8) && !lcd_aa && !fd->msdf) {
				modulate.r = modulate.g = modulate.b = 1.0;
			}
#endif
			if (RenderingServer::get_singleton() != nullptr) {
				if (fd->cache[size]->textures[gl.texture_idx].dirty) {
					ShelfPackTexture &tex = fd->cache[size]->textures.write[gl.texture_idx];
					Ref<Image> img = Image::create_from_data(tex.texture_w, tex.texture_h, false, tex.format, tex.imgdata);
					if (fd->mipmaps) {
						img->generate_mipmaps();
					}
					if (tex.texture.is_null()) {
						tex.texture = ImageTexture::create_from_image(img);
					} else {
						tex.texture->update(img);
					}
					tex.dirty = false;
				}
				RID texture = fd->cache[size]->textures[gl.texture_idx].texture->get_rid();