### 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)

ShapedTextDataAdvanced *sd = shaped_owner.get_or_null(p_shaped);
	ERR_FAIL_COND_V(!sd, false);
	MutexLock lock(sd->mutex);
	if (sd->valid) {
		return true;
	}
	invalidate(sd, false);
	if (sd->parent != RID()) {
		_shaped_text_shape(sd->parent);
		ShapedTextDataAdvanced *parent_sd = shaped_owner.get_or_null(sd->parent);
		ERR_FAIL_COND_V(!parent_sd->valid, false);
		ERR_FAIL_COND_V(!_shape_substr(sd, parent_sd, sd->start, sd->end - sd->start), false);
		return true;
	}
	if (sd->text.length(
		sd->valid = true;
		return true;
	}
	sd->utf16 = sd->text.utf16();
	const UChar *data = sd->utf16.get_data();
	
	if (sd->script_iter == nullptr) {
		sd->script_iter = memnew(ScriptIterator(sd->text, 0, sd->text.length()));
	}
	int base_para_direction = UBIDI_DEFAULT_LTR;
	switch (sd->direction) {
		case DIRECTION_LTR: {
			sd->para_direction = DIRECTION_LTR;