Revert board weight changes from `nil` to `-1`
Problem to solve
Some of the boards were modified with a database migration that needs to be reverted, but it can't just be reversed in the obvious way.
Related reversion MR:
- Original MR (EE): https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14180
- Original MR (CE port): !14586 (closed)
- Weight reversion issue: https://gitlab.com/gitlab-org/gitlab-ee/issues/13337
- Original reversion issue (refers to Milestone): https://gitlab.com/gitlab-org/gitlab-ce/issues/65676
What does success look like, and how can we measure that?
The boards that had
-1 before this migration was run have
-1 restored as their