See https://github.com/ppy/osu/pull/30215#issuecomment-2407775408 for
context.
Turns out the test failures were more correct than I'd thought. The
long-and-short of it is that both in "pure random" mode and in
"permutation" mode, when running out of track history to fall
back on, it was possible for the random algorithm to pick the same song
twice in a row - which is probably not desired, and which this explicit
exclude should make impossible.