Bump Ruby version in RuboCop workflow to 4.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

.github/workflows/rubocop.yml

@@ -18,7 +18,7 @@ jobs:
     - name: Set up Ruby 3.1
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: "3.1"
+        ruby-version: "4.0"
     - name: Install required package
       run: |
         sudo apt-get install alien