www/gitlab: decouple from www/rubygem-rqrcode

This makes it possible to upgrade www/rubygem-rqrcode to version 3
which unbreaks it due to update of www/rubygem-rqrcode_core.

PR: 286372
(cherry picked from commit e5bf2131ff5710c26771c6c6a4d2541653c11436)