### 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)

#endif
	UErrorCode status = U_ZERO_ERROR;
	int64_t match_index = -1;
	Char16String utf16 = p_string.utf16();
	Vector<UChar *> skeletons;
	skeletons.resize(p_dict.size());
	USpoofChecker *sc = uspoof_open(&status);
	uspoof_setChecks(sc, USPOOF_CONFUSABLE, &status);
	for (int i = 0; i < p_dict.size(); i++) {
		Char16String word = p_dict[i].utf16();
		int32_t len = uspoof_getSkeleton(sc, 0, word.get_data(), -1, NULL, 0, &status);
		skeletons.write[i] = (UChar *)memalloc(++len * sizeof(UChar));
		status = U_ZERO_ERROR;
		uspoof_getSkeleton(sc, 0, word.get_data(), -1, skeletons.write[i], len, &status);
	}
	int32_t len = uspoof_getSkeleton(sc, 0, utf16.get_data(), -1, NULL, 0, &status);
	UChar *skel = (UChar *)memalloc(++len * sizeof(UChar));
	status = U_ZERO_ERROR;
	uspoof_getSkeleton(sc, 0, utf16.get_data(), -1, skel, len, &status);
	for (int i = 0; i < skeletons.size(); i++) {
		if (u_strcmp(skel, skeletons[i]
			match_index = i;
			
		}
	}
	memfree(skel);
	for (int i = 0; i < skeletons.size(); i++) {
		memfree(skeletons.write[i]);
	}
	uspoof_close(sc);