### 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)

Array fonts_no_match;
							int font_count = span.fonts.size();
							if (font_count > 0) {
								fonts.push_back(sd->spans[k].fonts[0]);
							}
							for (int l = 1; l < font_count; l++) {
								if (_font_is_script_supported(span.fonts[l], script_code)) {
									if (_font_is_language_supported(span.fonts[l], span.language)) {
										fonts.push_back(sd->spans[k].fonts[l]);
									} else {
										fonts_scr_only.push_back(sd->spans[k].fonts[l]);
									}
								} else {
									fonts_no_match.push_back(sd->spans[k].fonts[l]);
								}
							}
							fonts.append_array(fonts_scr_only);
							fonts.append_array(fonts_no_match);
							_shape_run(sd, MAX(sd->spans[k].start - sd->start, script_run_start), MIN(sd->spans[k].end - sd->start, script_run_end), sd->script_iter->script_ranges[j].script, bidi_run_direction, fonts, k, 0, 0, 0);
						}
					}
				}
			}
		}
	}
	_realign(sd);
	sd->valid = true;
	return sd->valid;
}
bool TextServerAdvanced::_shaped_text_is_ready(const RID &p_shaped) const {