Switch published attachment report to use attachment date
Switch published attachment report to use attachment date

The Data Standards Authority have asked us to change the date included
in the published attachments report (introduced in
https://github.com/alphagov/whitehall/pull/6148) to be the attachment
update date, rather than the date the edition was first published.

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall