Follow up - 0798e7d47ed2505ea43dccdb9c1ef867d700f720 - moved from circle ci to github actions. (Re-)enable rubocop.

.github/ci.sh

@@ -34,7 +34,7 @@ gem install bundler:1.7.3
 bundle install --without "${INSTALL_OPTION}"
 
 # unit tests
-# bundle exec rubocop
+bundle exec rubocop
 bundle exec rake zammad:db:init
 bundle exec rspec -t ~type:system -t ~searchindex
 bundle exec rake zammad:db:reset