I managed to do this by accident three times today while testing using
the dashboard display, so it's time to action on it.
Touched on in
https://github.com/ppy/osu/discussions/30740#discussioncomment-11345996.
Was also mentioned recently in discord or another discussion explicitly
but I can't find that.
The intention here is to make things more testable going forward.
Specifically, to remove the "back-door" entrance into `BeatmapCarousel`
where `BeatmapSets` can be set by tests and bypas/block realm retrieval.