### 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)

for (unsigned int j = last_cluster_index; j < i; j++) {
						w[j].end = glyph_info[i].cluster;
					}
				}
				if (p_direction == HB_DIRECTION_RTL || p_direction == HB_DIRECTION_BTT) {
					w[last_cluster_index].flags |= GRAPHEME_IS_RTL;
				}
				if (last_cluster_valid) {
					w[last_cluster_index].flags |= GRAPHEME_IS_VALID;
				}
				w[last_cluster_index].count = i - last_cluster_index;
				last_cluster_index = i;
				last_cluster_valid = true;
			}
			last_cluster_id = glyph_info[i].cluster;
			Glyph &gl = w[i];
			gl = Glyph();
			gl.start = glyph_info[i].cluster;
			gl.end = end;
			gl.count = 0;
			gl.font_rid = f;
			gl.font_size = fs;
			if (glyph_info[i].mask & HB_GLYPH_FLAG_UNSAFE_TO_BREAK) {
				gl.flags |= GRAPHEME_IS_CONNECTED;
			}
#if HB_VERSION_ATLEAST(5, 1, 0)
			if (glyph_info[i].mask & HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL) {
				gl.flags |= GRAPHEME_IS_SAFE_TO_INSERT_TATWEEL;
			}
#endif