### 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, Size2());
	MutexLock lock(fd->mutex);
	Vector2i size = _get_size_outline(fd, p_size);
	ERR_FAIL_COND_V(!_ensure_cache_for_size(fd, size), Size2());
	int mod = 0;
	if (fd->antialiasing == FONT_ANTIALIASING_LCD) {
		TextServer::FontLCDSubpixelLayout layout = (TextServer::FontLCDSubpixelLayout)(int)GLOBAL_GET("gui/theme/lcd_subpixel_layout");
		if (layout != FONT_LCD_SUBPIXEL_LAYOUT_NONE) {
			mod = (layout << 24);
		}
	}
	if (!_ensure_glyph(fd, size, p_glyph | mod)) {
		return Size2(); 
	}
	const HashMap<int32_t, FontGlyph> &gl = fd->cache[size]->glyph_map;
	ERR_FAIL_COND_V(gl[p_glyph | mod].texture_idx < -1 || gl[p_glyph | mod].texture_idx >= fd->cache[size]->textures.size(), Size2());
	if (RenderingServer::get_singleton() != nullptr) {
		if (gl[p_glyph | mod].texture_idx != -1) {
			if (fd->cache[size]->textures[gl[p_glyph | mod].texture_idx].dirty) {
				ShelfPackTexture &tex = fd->cache[size]->textures.write[gl[p_glyph | mod].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);
				}