### 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)

main = memnew(ItemFrame);
	main->index = 0;
	current = main;
	main->lines.resize(1);
	main->lines[0].from = main;
	main->first_invalid_line.store(0);
	main->first_resized_line.store(0);
	main->first_invalid_font_line.store(0);
	current_frame = main;
	vscroll = memnew(VScrollBar);
	add_child(vscroll, false, INTERNAL_MODE_FRONT);
	vscroll->set_drag_node(String(".."));
	vscroll->set_step(1);
	vscroll->set_anchor_and_offset(SIDE_TOP, ANCHOR_BEGIN, 0);
	vscroll->set_anchor_and_offset(SIDE_BOTTOM, ANCHOR_END, 0);
	vscroll->set_anchor_and_offset(SIDE_RIGHT, ANCHOR_END, 0);
	vscroll->connect("value_changed", callable_mp(this, &RichTextLabel::_scroll_changed));
	vscroll->set_step(1);
	vscroll->hide();
	set_text(p_text);
	updating.store(false);
	stop_thread.store(false);
	set_clip_contents(true);
}
RichTextLabel::~RichTextLabel() {
	_stop_thread();
	memdelete(main);
}