Administration: Correct alignment of meta boxes on the Edit screen with classic editor.

Follow-up to [61646], [61759].

Props umeshnevase, sabernhardt, SergeyBiryukov.
Fixes #65141.

git-svn-id: https://develop.svn.wordpress.org/trunk@62284 602fd350-edb4-49c9-b593-d223f7449a82