Administration: Correct alignment of the "PHP Update Required" dashboard box title.

Restore one instance of `!important` CSS rule for backward compatibility.

Follow-up to [48129], [48373].

Props whyisjake, sabernhardt, TimothyBlynJacobs, SergeyBiryukov.
Fixes #50788.
Built from https://develop.svn.wordpress.org/trunk@48671


git-svn-id: https://core.svn.wordpress.org/trunk@48433 1a063a9b-81f0-0310-95a4-ce76da25c4cd