### 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 spn_to = (is_rtl) ? sd->spans.size() : -1;
					int spn_delta = (is_rtl) ? +1 : -1;
					for (int k = spn_from; k != spn_to; k += spn_delta) {
						const ShapedTextDataAdvanced::Span &span = sd->spans[k];
						if (span.start - sd->start >= script_run_end || span.end - sd->start <= script_run_start) {
							continue;
						}
						if (span.embedded_key != Variant()) {
							
							if (sd->orientation == ORIENTATION_HORIZONTAL) {
								sd->objects[span.embedded_key].rect.position.x = sd->width;
								sd->width += sd->objects[span.embedded_key].rect.size.x;
							} else {
								sd->objects[span.embedded_key].rect.position.y = sd->width;
								sd->width += sd->objects[span.embedded_key].rect.size.y;
							}
							Glyph gl;
							gl.start = span.start;
							gl.end = span.end;
							gl.count = 1;
							gl.flags = GRAPHEME_IS_VALID | GRAPHEME_IS_VIRTUAL;
							if (sd->orientation == ORIENTATION_HORIZONTAL) {
								gl.advance = sd->objects[span.embedded_key].rect.size.x;
							} else {
								gl.advance = sd->objects[span.embedded_key].rect.size.y;
							}
							sd->glyphs.push_back(gl);
						} else {
							Array fonts;
							Array fonts_scr_only;