Admin Reskin: Correct hover color for links on the login screen.

Follow-up to [61681].

Reviewed by wildworks, SergeyBiryukov.

Props nikunj8866, wildworks, joedolson, audrasjb, huzaifaalmesbah, shailu25, ozgursar, noruzzaman, khushi1501, SergeyBiryukov.
Fixes #64879.

git-svn-id: https://develop.svn.wordpress.org/trunk@62113 602fd350-edb4-49c9-b593-d223f7449a82