Danger GitLab reference check should be more precise

The following discussion from !8960 (merged) should be addressed:

• @godfat started a discussion:

  Danger says Use full URLs instead of short references (`gitlab-org/gitlab-ce#123` or `!123`), as short references are displayed as plain text outside of GitLab but this doesn't make sense. The message was:

  Properly override sign_in_and_redirect with right arity
  
  for `Devise::Controllers::Helpers#sign_in_and_redirect`,
  which has arity of -2:
  https://www.rubydoc.info/github/plataformatec/devise/Devise%2FControllers%2FHelpers:sign_in_and_redirect

  There's no reference to any issue.