### 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)

if (p_direction == HB_DIRECTION_RTL || p_direction == HB_DIRECTION_BTT) {
		gl.flags |= TextServer::GRAPHEME_IS_RTL;
	}
	gl.font_rid = p_font;
	gl.font_size = p_font_size;
	if (glyph_count > 0) {
		if (p_sd->orientation == ORIENTATION_HORIZONTAL) {
			if (subpos) {
				gl.advance = (double)glyph_pos[0].x_advance / (64.0 / scale) + _get_extra_advance(p_font, p_font_size);
			} else {
				gl.advance = Math::round((double)glyph_pos[0].x_advance / (64.0 / scale) + _get_extra_advance(p_font, p_font_size));
			}
		} else {
			gl.advance = -Math::round((double)glyph_pos[0].y_advance / (64.0 / scale));
		}
		gl.count = 1;
		gl.index = glyph_info[0].codepoint;
		if (subpos) {
			gl.x_off = (double)glyph_pos[0].x_offset / (64.0 / scale);
		} else {
			gl.x_off = Math::round((double)glyph_pos[0].x_offset / (64.0 / scale));
		}
		gl.y_off = -Math::round((double)glyph_pos[0].y_offset / (64.0 / scale));
		if ((glyph_info[0].codepoint != 0) || !u_isgraph(p_char)) {
			gl.flags |= GRAPHEME_IS_VALID;
		}
	}
	return gl;
}
_FORCE_INLINE_ void TextServerAdvanced::_add_featuers(const Dictionary &p_source, Vector<hb_feature_t> &r_ftrs) {