Fix Ruby version in RuboCop workflow step name

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

Author: yahonda

.github/workflows/rubocop.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up Ruby 3.1
+    - name: Set up Ruby 4.0
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: "4.0"