### 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 (r_click_item) {
		*r_click_item = nullptr;
	}
	if (r_click_char != nullptr) {
		*r_click_char = 0;
	}
	if (r_outside != nullptr) {
		*r_outside = true;
	}
	Size2 size = get_size();
	Rect2 text_rect = _get_text_rect();
	int vofs = vscroll->get_value();
	
	int to_line = main->first_invalid_line.load();
	int from_line = _find_first_line(0, to_line, vofs);
	Point2 ofs = text_rect.get_position() + Vector2(0, main->lines[from_line].offset.y - vofs);
	while (ofs.y < size.height && from_line < to_line) {
		MutexLock lock(main->lines[from_line].text_buf->get_mutex());
		_find_click_in_line(p_frame, from_line, ofs, text_rect.size.x, p_click, r_click_frame, r_click_line, r_click_item, r_click_char, false, p_meta);
		ofs.y += main->lines[from_line].text_buf->get_size().y + main->lines[from_line].text_buf->get_line_count() * theme_cache.line_separation;
		if (((r_click_item != nullptr) && ((*r_click_item) != nullptr)) || ((r_click_frame != nullptr) && ((*r_click_frame) != nullptr))) {
			if (r_outside != nullptr) {
				*r_outside = false;
			}
			return;
		}
		from_line++;
	}
}
float RichTextLabel::_find_click_in_line(ItemFrame *p_frame, int p_line, const Vector2 &p_ofs, int p_width, const Point2i &p_click, ItemFrame **r_click_frame, int *r_click_line, Item **r_click_item, int *r_click_char, bool p_table, bool p_meta) {