### 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 (!f.is_valid()) {
					if (system_fonts.has(key)) {
						const SystemFontCache &sysf_cache = system_fonts[key];
						if (sysf_cache.max_var == sysf_cache.var.size()) {
							
							continue;
						}
					}
					if (!system_font_data.has(E)) {
						system_font_data[E] = FileAccess::get_file_as_bytes(E);
					}
					const PackedByteArray &font_data = system_font_data[E];
					SystemFontCacheRec sysf;
					sysf.rid = _create_font();
					_font_set_data_ptr(sysf.rid, font_data.ptr(), font_data.size());
					Dictionary var = dvar;
					
					int best_score = 0;
					int best_match = -1;
					for (int face_idx = 0; face_idx < _font_get_face_count(sysf.rid); face_idx++) {
						_font_set_face_index(sysf.rid, face_idx);
						if (unlikely(!_font_has_char(sysf.rid, text[0]))) {
							continue;
						}
						BitField<FontStyle> style = _font_get_style(sysf.rid);
						int weight = _font_get_weight(sysf.rid);
						int stretch = _font_get_stretch(sysf.rid);
						int score = (20 - Math::abs(weight - font_weight) / 50);