### 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)

tex.dirty = false;
			}
			return fd->cache[size]->textures[gl[p_glyph | mod].texture_idx].texture->get_size();
		}
	}
	return Size2();
}
Dictionary TextServerAdvanced::_font_get_glyph_contours(const RID &p_font_rid, int64_t p_size, int64_t p_index) const {
	FontAdvanced *fd = font_owner.get_or_null(p_font_rid);
	ERR_FAIL_COND_V(!fd, Dictionary());
	MutexLock lock(fd->mutex);
	Vector2i size = _get_size(fd, p_size);
	ERR_FAIL_COND_V(!_ensure_cache_for_size(fd, size), Dictionary());
#ifdef MODULE_FREETYPE_ENABLED
	PackedVector3Array points;
	PackedInt32Array contours;
	int32_t index = p_index & 0xffffff; 
	int error = FT_Load_Glyph(fd->cache[size]->face, index, FT_LOAD_NO_BITMAP | (fd->force_autohinter ? FT_LOAD_FORCE_AUTOHINT : 0));
	ERR_FAIL_COND_V(error, Dictionary());
	if (fd->embolden != 0.f) {
		FT_Pos strength = fd->embolden * p_size * 4; 
		FT_Outline_Embolden(&fd->cache[size]->face->glyph->outline, strength);
	}
	if (fd->transform != Transform2D()) {
		FT_Matrix mat = { FT_Fixed(fd->transform[0][0] * 65536), FT_Fixed(fd->transform[0][1] * 65536), FT_Fixed(fd->transform[1][0] * 65536), FT_Fixed(fd->transform[1][1] * 65536) }; 
		FT_Outline_Transform(&fd->cache[size]->face->glyph->outline, &mat);
	}
	double scale = (1.0 / 64.0) / fd->cache[size]->oversampling * fd->cache[size]->scale;
	if (fd->msdf) {
		scale = scale * (double)p_size / (double)fd->msdf_source_size;