Add index on updated_at to public body versions as this is how they are retrieved in the admin timeline view.
user
```ruby
class AddUpdatedAtIndexToPublicBodyVersions < ActiveRecord::Migration
  def self.up
      add_index :public_body_versions, :updated_at
  end

  def self.down
      remove_index :public_body_versions, :updated_at
  end
end
```
assistant