Run wp_auth_check on every heartbeat tick.

wp_heartbeat_received only runs when data is sent. We want to always pass this data back, though.

fixes #27081.

Built from https://develop.svn.wordpress.org/trunk@27153


git-svn-id: http://core.svn.wordpress.org/trunk@27020 1a063a9b-81f0-0310-95a4-ce76da25c4cd