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.
Didn't really work to fix these tests due to the sticky nature of the
failure. Also I can no longer reproduce locally, so the hope is that
these are fixed by https://github.com/ppy/osu/pull/30634.