### 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)

}
					yofs += frame->padding.size.y;
					offset.x += table->columns[column].width + theme_cache.table_h_separation + frame->padding.size.x;
					row_height = MAX(yofs, row_height);
					if (column == col_count - 1) {
						offset.x = 0;
						row_height += theme_cache.table_v_separation;
						table->total_height += row_height;
						offset.y += row_height;
						table->rows.push_back(row_height);
						table->rows_baseline.push_back(table->total_height - row_height + row_baseline);
						row_height = 0;
					}
					idx++;
				}
				int row_idx = (table->align_to_row < 0) ? table->rows_baseline.size() - 1 : table->align_to_row;
				if (table->rows_baseline.size() != 0 && row_idx < (int)table->rows_baseline.size() - 1) {
					l.text_buf->resize_object((uint64_t)it, Size2(table->total_width, table->total_height), table->inline_align, Math::round(table->rows_baseline[row_idx]));
				} else {
					l.text_buf->resize_object((uint64_t)it, Size2(table->total_width, table->total_height), table->inline_align);
				}
			} break;
			default:
				break;
		}
	}
	l.offset.y = p_h;
	return _calculate_line_vertical_offset(l);
}
float RichTextLabel::_shape_line(ItemFrame *p_frame, int p_line, const Ref<Font> &p_base_font, int p_base_font_size, int p_width, float p_h, int *r_char_offset) {