fix ruby version in CI

.gitlab-ci.yml

@@ -1,6 +1,6 @@
 before_script:
   - apt-get update -qy
-    - apt-get install -y ruby git
+  - apt-get install -y git
   - gem install dpl
   - curl https://cli-assets.heroku.com/install.sh | sh
 
@@ -9,7 +9,7 @@ stages:
 
 deploy_production:
   stage: deploy
-    image: ruby:latest
+  image: ruby:3.0.1
   script:
     - dpl --provider=heroku --app=$HEROKU_APP_PRODUCTION --api-key=$HEROKU_API_KEY
     - heroku run bundle exec rails db:migrate --exit-code --app $HEROKU_APP_PRODUCTION