Fix keyboard accessibility for row actions in list tables. Restore the CSS part of [25592], accidentally reverted in [26072].

fixes #26145.
Built from https://develop.svn.wordpress.org/trunk@26324


git-svn-id: http://core.svn.wordpress.org/trunk@26227 1a063a9b-81f0-0310-95a4-ce76da25c4cd