### 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)

p_font_data->font_name = String::utf8((const char *)fd->face->family_name);
			}
			if (fd->face->style_name != nullptr) {
				p_font_data->style_name = String::utf8((const char *)fd->face->style_name);
			}
			p_font_data->weight = _font_get_weight_by_name(p_font_data->style_name.to_lower());
			p_font_data->stretch = _font_get_stretch_by_name(p_font_data->style_name.to_lower());
			p_font_data->style_flags = 0;
			if ((fd->face->style_flags & FT_STYLE_FLAG_BOLD) || p_font_data->weight >= 700) {
				p_font_data->style_flags.set_flag(FONT_BOLD);
			}
			if ((fd->face->style_flags & FT_STYLE_FLAG_ITALIC) || _is_ital_style(p_font_data->style_name.to_lower())) {
				p_font_data->style_flags.set_flag(FONT_ITALIC);
			}
			if (fd->face->face_flags & FT_FACE_FLAG_FIXED_WIDTH) {
				p_font_data->style_flags.set_flag(FONT_FIXED_WIDTH);
			}
			hb_face_t *hb_face = hb_font_get_face(fd->hb_handle);
			
			p_font_data->supported_scripts.clear();
			unsigned int count = hb_ot_layout_table_get_script_tags(hb_face, HB_OT_TAG_GSUB, 0, nullptr, nullptr);
			if (count != 0) {
				hb_tag_t *script_tags = (hb_tag_t *)memalloc(count * sizeof(hb_tag_t));
				hb_ot_layout_table_get_script_tags(hb_face, HB_OT_TAG_GSUB, 0, &count, script_tags);
				for (unsigned int i = 0; i < count; i++) {
					p_font_data->supported_scripts.insert(script_tags[i]);
				}
				memfree(script_tags);
			}
			count = hb_ot_layout_table_get_script_tags(hb_face, HB_OT_TAG_GPOS, 0, nullptr, nullptr);