Update pull_request.yml

Author: kenyonj

.github/workflows/pull_request.yml

@@ -10,7 +10,7 @@ jobs:
     - name: Setup Ruby
       uses: actions/setup-ruby@v1
       with:
-        ruby-version: 2.7
+        ruby-version: 3.1
     - name: Install bundler
       run: |
         gem install bundler:2.1.4