### 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)

score += (20 - Math::abs(stretch - font_stretch) / 10);
						if (bool(style & TextServer::FONT_ITALIC) == bool(font_style & TextServer::FONT_ITALIC)) {
							score += 30;
						}
						if (score >= best_score) {
							best_score = score;
							best_match = face_idx;
						}
						if (best_score == 70) {
							
						}
					}
					if (best_match == -1) {
						_free_rid(sysf.rid);
						continue;
					} else {
						_font_set_face_index(sysf.rid, best_match);
					}
					sysf.index = best_match;
					
					if (best_score != 70) {
						Dictionary ftr = _font_supported_variation_list(sysf.rid);
						if (ftr.has(wdth_tag)) {
							var[wdth_tag] = font_stretch;
							_font_set_stretch(sysf.rid, font_stretch);
						}
						if (ftr.has(wgth_tag)) {
							var[wgth_tag] = font_weight;
							_font_set_weight(sysf.rid, font_weight);
						}