### 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 ((font_style & TextServer::FONT_ITALIC) && ftr.has(ital_tag)) {
							var[ital_tag] = 1;
							_font_set_style(sysf.rid, _font_get_style(sysf.rid) | TextServer::FONT_ITALIC);
						}
					}
					_font_set_antialiasing(sysf.rid, key.antialiasing);
					_font_set_generate_mipmaps(sysf.rid, key.mipmaps);
					_font_set_multichannel_signed_distance_field(sysf.rid, key.msdf);
					_font_set_msdf_pixel_range(sysf.rid, key.msdf_range);
					_font_set_msdf_size(sysf.rid, key.msdf_source_size);
					_font_set_fixed_size(sysf.rid, key.fixed_size);
					_font_set_force_autohinter(sysf.rid, key.force_autohinter);
					_font_set_hinting(sysf.rid, key.hinting);
					_font_set_subpixel_positioning(sysf.rid, key.subpixel_positioning);
					_font_set_variation_coordinates(sysf.rid, var);
					_font_set_oversampling(sysf.rid, key.oversampling);
					_font_set_embolden(sysf.rid, key.embolden);
					_font_set_transform(sysf.rid, key.transform);
					if (system_fonts.has(key)) {
						system_fonts[key].var.push_back(sysf);
					} else {
						SystemFontCache &sysf_cache = system_fonts[key];
						sysf_cache.max_var = _font_get_face_count(sysf.rid);
						sysf_cache.var.push_back(sysf);
					}
					f = sysf.rid;
				}
				
			}
		}