### Godot version

2992ffd25523cb8b3e0ef1b873c40115b8940178

### System information

Windows 10

### Issue description

Godot crashes randomly within a few seconds after project start when moving with the mouse.

![win_err](https://github.com/godotengine/godot/assets/52464204/1da28596-d95b-40f3-b32f-12219ec02c5d)

Started after recent merge of https://github.com/godotengine/godot/pull/67791.
I can confirm that reverting the pr fixes the crashes.

### Steps to reproduce

see desc

### Minimal reproduction project

N/A
ERR_MAIN_THREAD_GUARD;
	switch (p_what) {
		case NOTIFICATION_POSTINITIALIZE: {
			initialized = true;
			_invalidate_theme_cache();
			_update_theme_item_cache();
		} break;
		case NOTIFICATION_PARENTED: {
			theme_owner->assign_theme_on_parented(this);
		} break;
		case NOTIFICATION_UNPARENTED: {
			theme_owner->clear_theme_on_unparented(this);
		} break;
		case NOTIFICATION_ENTER_TREE: {
			bool embedded = false;
			{
				embedder = get_embedder();
				if (embedder) {
					embedded = true;
					if (!visible) {