### 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)

Vector2 off;
	bool line_clicked = false;
	float text_rect_begin = 0.0;
	int char_pos = -1;
	Line &l = p_frame->lines[p_line];
	MutexLock lock(l.text_buf->get_mutex());
	bool rtl = (l.text_buf->get_direction() == TextServer::DIRECTION_RTL);
	bool lrtl = is_layout_rtl();
	
	bool table_hit = false;
	Vector2i table_range;
	float table_offy = 0.f;
	ItemFrame *table_click_frame = nullptr;
	int table_click_line = -1;
	Item *table_click_item = nullptr;
	int table_click_char = -1;
	for (int line = 0; line < l.text_buf->get_line_count(); line++) {
		RID rid = l.text_buf->get_line_rid(line);
		float width = l.text_buf->get_width();