### 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)

} 
		case FT_PIXEL_MODE_LCD: {
			color_size = 4;
			w /= 3;
		} 
		case FT_PIXEL_MODE_LCD_V: {
			color_size = 4;
			h /= 3;
		} 
	}
	int mw = w + p_rect_margin * 4;
	int mh = h + p_rect_margin * 4;
	ERR_FAIL_COND_V(mw > 4096, FontGlyph());
	ERR_FAIL_COND_V(mh > 4096, FontGlyph());
	Image::Format require_format = color_size == 4 ? Image::FORMAT_RGBA8 : Image::FORMAT_LA8;
	FontTexturePosition tex_pos = find_texture_pos_for_glyph(p_data, color_size, require_format, mw, mh, false);
	ERR_FAIL_COND_V(tex_pos.index < 0, FontGlyph());
	
	ShelfPackTexture &tex = p_data->textures.write[tex_pos.index];
	{
		uint8_t *wr = tex.imgdata.ptrw();
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				int ofs = ((i + tex_pos.y + p_rect_margin * 2) * tex.texture_w + j + tex_pos.x + p_rect_margin * 2) * color_size;
				ERR_FAIL_COND_V(ofs >= tex.imgdata.size(), FontGlyph());
				switch (bitmap.pixel_mode) {
					case FT_PIXEL_MODE_MONO: {
						int byte = i * bitmap.pitch + (j >> 3);
						int bit = 1 << (7 - (j % 8));
						wr[ofs + 0] = 255;