### 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)

hb_font_t *hb_font = _font_get_hb_handle(p_font, p_font_size);
	double scale = _font_get_scale(p_font, p_font_size);
	bool subpos = (scale != 1.0) || (_font_get_subpixel_positioning(p_font) == SUBPIXEL_POSITIONING_ONE_HALF) || (_font_get_subpixel_positioning(p_font) == SUBPIXEL_POSITIONING_ONE_QUARTER) || (_font_get_subpixel_positioning(p_font) == SUBPIXEL_POSITIONING_AUTO && p_font_size <= SUBPIXEL_POSITIONING_ONE_HALF_MAX_SIZE);
	ERR_FAIL_COND_V(hb_font == nullptr, Glyph());
	hb_buffer_clear_contents(p_sd->hb_buffer);
	hb_buffer_set_direction(p_sd->hb_buffer, p_direction);
	hb_buffer_set_flags(p_sd->hb_buffer, (hb_buffer_flags_t)(HB_BUFFER_FLAG_DEFAULT));
	hb_buffer_set_script(p_sd->hb_buffer, p_script);
	hb_buffer_add_utf32(p_sd->hb_buffer, (const uint32_t *)&p_char, 1, 0, 1);
	hb_shape(hb_font, p_sd->hb_buffer, nullptr, 0);
	unsigned int glyph_count = 0;
	hb_glyph_info_t *glyph_info = hb_buffer_get_glyph_infos(p_sd->hb_buffer, &glyph_count);
	hb_glyph_position_t *glyph_pos = hb_buffer_get_glyph_positions(p_sd->hb_buffer, &glyph_count);
	
	Glyph gl;