Order Fatality Notices by first published date

Order the Fatality Notices by first published date, instead of last updated date. Change the test to ensure order remains when a Fatality Notice is updated.
can we change this to:
```
new_iraq_fatality.update_column(:first_published_at, 5.days.ago)
new_iraq_fatality.update_column(:public_timestamp, 3.days.ago)
```
it is not realistic that something with a public timestamp of `2.weeks.ago` was first published `2.days.ago`. we try and keep test data as close to real world scenarios, and it also ensures that the test doesn't need to be updated incase validations are introduced in future for this condition.