Make the list of gallery attachments in the "old iframe media modal" break less. The "columns" are not aligned with the headers, but this would require a markup rewrite of a deprecated feature.

Fixes #28098.


Built from https://develop.svn.wordpress.org/trunk@28829


git-svn-id: http://core.svn.wordpress.org/trunk@28633 1a063a9b-81f0-0310-95a4-ce76da25c4cd