chore: gha: use newer ruby for rubocop, rbs and steep

Author: rarruda

.github/workflows/pull_request.yml

@@ -14,7 +14,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: "3.0"
+        ruby-version: "3.1"
         bundler-cache: true
     - name: Run RuboCop
       run: bundle exec rubocop