Fix an out-of-order issue in the new update-during-publish behavior

Summary:
Ref T13552. The Herald field "Accepted Differential revision" (and similar fields) depend on the task/revision update steps running before Herald executes.

Herald currently executes first, so it never sees associated revisions. Swap this order.

Test Plan: Published a commit, got a clean parse/import. Will test with production rules ("Cowboy Commits").

Maniphest Tasks: T13552

Differential Revision: https://secure.phabricator.com/D21468