### 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)

accept_event();
			}
		}
	}
	Ref<InputEventMouseMotion> m = p_event;
	if (m.is_valid()) {
		ItemFrame *c_frame = nullptr;
		int c_line = 0;
		Item *c_item = nullptr;
		int c_index = 0;
		bool outside;
		_find_click(main, m->get_position(), &c_frame, &c_line, &c_item, &c_index, &outside, false);
		if (selection.click_item && c_item) {
			selection.from_frame = selection.click_frame;
			selection.from_line = selection.click_line;
			selection.from_item = selection.click_item;
			selection.from_char = selection.click_char;
			selection.to_frame = c_frame;
			selection.to_line = c_line;
			selection.to_item = c_item;
			selection.to_char = c_index;
			bool swap = false;
			if (selection.click_frame && c_frame) {
				const Line &l1 = c_frame->lines[c_line];
				const Line &l2 = selection.click_frame->lines[selection.click_line];
				if (l1.char_offset + c_index < l2.char_offset + selection.click_char) {
					swap = true;
				} else if (l1.char_offset + c_index == l2.char_offset + selection.click_char) {
					deselect();
					return;