Notify w-b earlier

Before Debian LTS started to use the security archive, all uploads that
would trigger buildds would be sourceful uploads to a policy queue. So
new packages entering the build queues and pushing the public mirrors
would likely not happen in the same cron.unchecked run.

With Debian LTS, uploads would go to both the build queues and trigger a
public mirror push. If the mirror push takes more than three minutes,
cron.buildd would however not notify w-b of changes.

This patch moves the w-b notification right behind the update of the
build queues and before the mirror push to avoid the problem. Ideally
we would not rely on anything happening within the last three minutes
though.