Fix `all_assignees_are_dev_role?`
What does this MR do and why?
修复问题: https://jihulab.com/gitlab-cn/gitlab/-/issues/1439#note_1477637
Follow up !94 (merged)
修复问题: https://jihulab.com/gitlab-cn/gitlab/-/issues/1439#note_1477637
Follow up !94 (merged)