### 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)

wr[ofs + 0] = bitmap.buffer[ofs_color + bitmap.pitch * 2];
							wr[ofs + 1] = bitmap.buffer[ofs_color + bitmap.pitch];
							wr[ofs + 2] = bitmap.buffer[ofs_color + 0];
							wr[ofs + 3] = 255;
						} else {
							wr[ofs + 0] = bitmap.buffer[ofs_color + 0];
							wr[ofs + 1] = bitmap.buffer[ofs_color + bitmap.pitch];
							wr[ofs + 2] = bitmap.buffer[ofs_color + bitmap.pitch * 2];
							wr[ofs + 3] = 255;
						}
					} 
					default:
						ERR_FAIL_V_MSG(FontGlyph(), "Font uses unsupported pixel format: " + String::num_int64(bitmap.pixel_mode) + ".");
						
				}
			}
		}
	}
	tex.dirty = true;
	FontGlyph chr;
	chr.advance = advance * p_data->scale / p_data->oversampling;
	chr.texture_idx = tex_pos.index;
	chr.found = true;
	chr.uv_rect = Rect2(tex_pos.x + p_rect_margin, tex_pos.y + p_rect_margin, w + p_rect_margin * 2, h + p_rect_margin * 2);
	chr.rect.position = Vector2(xofs - p_rect_margin, -yofs - p_rect_margin) * p_data->scale / p_data->oversampling;
	chr.rect.size = chr.uv_rect.size * p_data->scale / p_data->oversampling;
	return chr;
}
#endif
_FORCE_INLINE_ bool TextServerAdvanced::_ensure_glyph(FontAdvanced *p_font_data, const Vector2i &p_size, int32_t p_glyph) const {