- In the final round of review (!5081), we moved the protected branch
  access levels from Rails enums to constants from Gitlab::Access.

- The migrations that moved us from the old data model (a single
  protected_branches table with developers_can_push and
  developers_can_merge flags) to the new one (separate tables for
  push_access_levels and merge_access_levels) was not updated.

- These migrations still used 0 to mean "Masters" and 1 to mean
  "Developers" (matching the previous Rails enum), while Gitlab::Access
  uses 40 and 30 for these, respectively.

- Once the migrations run, our data gets into a broken state.

- We fix this by migrating all `0`s to `40` and all `1`s to `30`.

- https://gitlab.com/gitlab-org/gitlab-ce/issues/20606#note_13561628

= Caveats =

- In Gitlab::Access, 0 represents NO_ACCESS. When we run this migration,
  all protected branches with "No one" as an access level will be
  changed to "Masters"