Update Ruby version in GitHub Actions workflow from 3.4.1 to 4.0

Author: berkos

.github/workflows/main.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Setup Ruby and install gems
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 3.4.1
+          ruby-version: 4.0
           bundler-cache: true
       - name: Run Rubocop
         run: bundle exec rubocop --parallel