1. Instantiate `ProtectedBranchesAccessSelect` from `dispatcher`
2. Use `can?(user, ...)` instead of `user.can?(...)`
3. Add `DOWNTIME` notes to all migrations added in !5081.
4. Add an explicit `down` method for migrations removing the
`developers_can_push` and `developers_can_merge` columns, ensuring that
the columns created (on rollback) have the appropriate defaults.
5. Remove duplicate CHANGELOG entries.
6. Blank lines after guard clauses.
