Add data migration to fix bad unpublishing
user
```ruby
Unpublishing.from_slug('assessment-and-reporting-arrangements-key-stage-2-2014', Publication).
  update_attributes({alternative_url: 'https://education.gov.uk/schools/teachingandlearning/assessment/keystage2/g00227867/ks2-assessment-reporting',
                     redirect: true})
```
assistant