### 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_line);
	ERR_FAIL_COND_MSG(!sd, "ShapedTextDataAdvanced invalid.");
	MutexLock lock(sd->mutex);
	if (!sd->valid) {
		_shaped_text_shape(p_shaped_line);
	}
	sd->text_trimmed = false;
	sd->overrun_trim_data.ellipsis_glyph_buf.clear();
	bool add_ellipsis = p_trim_flags.has_flag(OVERRUN_ADD_ELLIPSIS);
	bool cut_per_word = p_trim_flags.has_flag(OVERRUN_TRIM_WORD_ONLY);
	bool enforce_ellipsis = p_trim_flags.has_flag(OVERRUN_ENFORCE_ELLIPSIS);
	bool justification_aware = p_trim_flags.has_flag(OVERRUN_JUSTIFICATION_AWARE);
	Glyph *sd_glyphs = sd->glyphs.ptrw();
	if ((p_trim_flags & OVERRUN_TRIM) == OVERRUN_NO_TRIM || sd_glyphs == nullptr || p_width <= 0 || !(sd->width > p_width || enforce_ellipsis)) {
		sd->overrun_trim_data.trim_pos = -1;
		sd->overrun_trim_data.ellipsis_pos = -1;
		return;
	}
	if (justification_aware && !sd->fit_width_minimum_reached) {
		return;
	}