False positive findings of button-class-haml-rb

This line is marked as a false positive by the scanner: https://gitlab.com/gitlab-org/gitlab/-/blob/d4872ce770675f05f90c97e755535854878240db/app/helpers/auth_helper.rb#L155

While it's a bit of a code smell (why is the gl-button-icon class being used on an image?), we don't have a migration strategy for it.