### 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)

p_new_sd->descent = MAX(p_new_sd->descent, Math::round(_font_get_glyph_advance(gl.font_rid, gl.font_size, gl.index).x * 0.5));
								}
							} else if (p_new_sd->preserve_invalid || (p_new_sd->preserve_control && is_control(gl.index))) {
								
								if (p_new_sd->orientation == ORIENTATION_HORIZONTAL) {
									p_new_sd->ascent = MAX(p_new_sd->ascent, get_hex_code_box_size(gl.font_size, gl.index).y);
								} else {
									p_new_sd->ascent = MAX(p_new_sd->ascent, Math::round(get_hex_code_box_size(gl.font_size, gl.index).x * 0.5));
									p_new_sd->descent = MAX(p_new_sd->descent, Math::round(get_hex_code_box_size(gl.font_size, gl.index).x * 0.5));
								}
							}
							p_new_sd->width += gl.advance * gl.repeat;
						}
						p_new_sd->glyphs.push_back(gl);
					}
				}
			}
		}
		_realign(p_new_sd);
	}
	p_new_sd->valid = true;
	return true;
}
RID TextServerAdvanced::_shaped_text_get_parent(const RID &p_shaped) const {
	ShapedTextDataAdvanced *sd = shaped_owner.get_or_null(p_shaped);
	ERR_FAIL_COND_V(!sd, RID());
	MutexLock lock(sd->mutex);
	return sd->parent;
}
double TextServerAdvanced::_shaped_text_fit_to_width(const RID &p_shaped, double p_width, BitField<TextServer::JustificationFlag> p_jst_flags) {