Add ruby image version. Error was "google-protobuf-3.21.12-x86_64-linux requires ruby version < 3.2.dev, >= 2.5, which is incompatible with the current version, ruby 3.2.0p0"

Update .gitlab-ci.yml ref: https://loumarven.dev/2020/02/23/getting-a-good-old-jekyll-theme-to-work-on-gitlab-pages/