### 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)

if (!is_inside_tree()) {
		return;
	}
	MutexLock data_lock(data_mutex);
	Rect2 text_rect = _get_text_rect();
	int ctrl_height = get_size().height;
	int fi = main->first_invalid_line.load();
	int total_chars = main->lines[fi].char_offset;
	float total_height = (fi == 0) ? 0 : _calculate_line_vertical_offset(main->lines[fi - 1]);
	for (int i = fi; i < (int)main->lines.size(); i++) {
		total_height = _shape_line(main, i, theme_cache.normal_font, theme_cache.normal_font_size, text_rect.get_size().width - scroll_w, total_height, &total_chars);
		updating_scroll = true;
		bool exceeds = total_height > ctrl_height && scroll_active;
		if (exceeds != scroll_visible) {
			if (exceeds) {
				scroll_visible = true;
				scroll_w = vscroll->get_combined_minimum_size().width;
				vscroll->show();
				vscroll->set_anchor_and_offset(SIDE_LEFT, ANCHOR_END, -scroll_w);
			} else {
				scroll_visible = false;
				scroll_w = 0;
				vscroll->hide();
			}
			main->first_invalid_line.store(0);
			main->first_resized_line.store(0);
			main->first_invalid_font_line.store(0);
			
			total_height = 0;