### 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)

table->rows_baseline.clear();
				Vector2 offset;
				float row_height = 0.0;
				for (Item *E : table->subitems) {
					ERR_CONTINUE(E->type != ITEM_FRAME); 
					ItemFrame *frame = static_cast<ItemFrame *>(E);
					int column = idx % col_count;
					offset.x += frame->padding.position.x;
					float yofs = frame->padding.position.y;
					float prev_h = 0;
					float row_baseline = 0.0;
					for (int i = 0; i < (int)frame->lines.size(); i++) {
						MutexLock sub_lock(frame->lines[i].text_buf->get_mutex());
						frame->lines[i].text_buf->set_width(table->columns[column].width);
						table->columns[column].width = MAX(table->columns[column].width, ceil(frame->lines[i].text_buf->get_size().x));
						frame->lines[i].offset.y = prev_h;
						float h = frame->lines[i].text_buf->get_size().y + (frame->lines[i].text_buf->get_line_count() - 1) * theme_cache.line_separation;
						if (i > 0) {
							h += theme_cache.line_separation;
						}
						if (frame->min_size_over.y > 0) {
							h = MAX(h, frame->min_size_over.y);
						}
						if (frame->max_size_over.y > 0) {
							h = MIN(h, frame->max_size_over.y);
						}
						yofs += h;
						prev_h = frame->lines[i].offset.y + frame->lines[i].text_buf->get_size().y + frame->lines[i].text_buf->get_line_count() * theme_cache.line_separation;
						frame->lines[i].offset += offset;
						row_baseline = MAX(row_baseline, frame->lines[i].text_buf->get_line_ascent(frame->lines[i].text_buf->get_line_count() - 1));