### 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)

}
			push_tornado(frequency, radius, connected);
			pos = brk_end + 1;
			tag_stack.push_front("tornado");
			set_process_internal(true);
		} else if (bbcode_name == "rainbow") {
			float saturation = 0.8f;
			OptionMap::Iterator saturation_option = bbcode_options.find("sat");
			if (saturation_option) {
				saturation = saturation_option->value.to_float();
			}
			float value = 0.8f;
			OptionMap::Iterator value_option = bbcode_options.find("val");
			if (value_option) {
				value = value_option->value.to_float();
			}
			float frequency = 1.0f;
			OptionMap::Iterator frequency_option = bbcode_options.find("freq");
			if (frequency_option) {
				frequency = frequency_option->value.to_float();
			}
			push_rainbow(saturation, value, frequency);
			pos = brk_end + 1;
			tag_stack.push_front("rainbow");
			set_process_internal(true);
		} else if (tag.begins_with("bgcolor=")) {
			String color_str = tag.substr(8, tag.length());
			Color color = Color::from_string(color_str, theme_cache.default_color);
			push_bgcolor(color);
			pos = brk_end + 1;