Fix appearance of sheared button borders after click
Fix appearance of sheared button borders after click

The border would previously get brighter after click, but then dim
instantly when the flash layer has fully faded out. The underlying issue
there is https://github.com/ppy/osu-framework/issues/5191, but
`ShearedButton` was placing the flashing layer incorrectly anyway, as
the intent was that it should also apply to the border.

NeoAdonis/osu,peppy/osu,peppy/osu,peppy/osu,NeoAdonis/osu,ppy/osu,ppy/osu,NeoAdonis/osu,ppy/osu