`TestLastPlayedUpdated` was implicitly relying on running first.
`TestGuestScoreIsStoredAsGuest` showing up changed test ordering,
causing the former test to fail if it didn't get to run first.
I'm not sure what the cause of the issue is, but I'm also not sure why
it wasn't using `DrawablePool` (was it not around back then?).
Either way, switching to a proper pool fixes things just fine.
Resolves https://github.com/ppy/osu/issues/25009.