RecentChangesUpdateJob: Fix GROUP BY

RecentChangesUpdateJob: Fix GROUP BY

When a column specified in GROUP BY is both a table column and a
SELECT-field, MySQL and PostgreSQL both interpret it as the table column
rather than the SELECT-field.

In PostgreSQL this raises an error, which is good since it lets us know
it needs fixing. But MySQL goes ahead and groups by the table field
which gives us the wrong result.

Bug: T230618
Change-Id: Id500556b2795b86849329eece3b651b08e29a7f7