Fixes issues as seen at
https://github.com/ppy/osu/runs/3023581865?check_suite_focus=true. Song
select may take a few frames to perform initial selection as there is a
bit of internal async logic. This ensures that the beatmap has been
updated before continuing with test execution.
These tests were manually pushing the `PlayerLoader` / `Player`
instances to `SongSelect`, which bypasses safeties in place which avoid
the exact issue that came up in https://github.com/ppy/osu/runs/2951759236
(see `AllowSelection` flag specifically).
