Update Ruby version into skunk.yml

Author: JuanVqz

.github/workflows/skunk.yml

@@ -10,7 +10,7 @@ jobs:
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 2.6
+          ruby-version: 3.1
           bundler-cache: true
       - name: Run test suite with COVERAGE=true
         run: |