### 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)

}
				}
			}
			int end = p_bbcode.find("[", brk_end);
			if (end == -1) {
				end = p_bbcode.length();
			}
			String image = p_bbcode.substr(brk_end + 1, end - brk_end - 1);
			Ref<Texture2D> texture = ResourceLoader::load(image, "Texture2D");
			if (texture.is_valid()) {
				Rect2 region;
				OptionMap::Iterator region_option = bbcode_options.find("region");
				if (region_option) {
					Vector<String> region_values = region_option->value.split(",", false);
					if (region_values.size() == 4) {
						region.position.x = region_values[0].to_float();
						region.position.y = region_values[1].to_float();
						region.size.x = region_values[2].to_float();
						region.size.y = region_values[3].to_float();
					}
				}
				Color color = Color(1.0, 1.0, 1.0);
				OptionMap::Iterator color_option = bbcode_options.find("color");
				if (color_option) {
					color = Color::from_string(color_option->value, color);
				}
				int width = 0;
				int height = 0;
				if (!bbcode_value.is_empty()) {
					int sep = bbcode_value.find("x");