This matches the expectation from stable where the popover also closes when you press enter. The side-effect is that spacebar also causes it to close, but luckily you don't need spacebar in the popover.
Spotted in passing when reviewing https://github.com/ppy/osu/pull/30080.
The popover would very arbitrarily revert to scaling by Y axis if both
checkboxes were checked off.
Not sure how this passed review.
It's not universally accepted here and a `when` crept in that can be
bypassed entirely using rather clean baseline language constructs, so
why bother at this point.