Update pull_request.yml

Author: kenyonj

.github/workflows/pull_request.yml

@@ -8,23 +8,10 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Setup Ruby
-      uses: actions/setup-ruby@v1
+      uses: ruby/setup-ruby@v1
       with:
         ruby-version: 3.1
-    - name: Install bundler
-      run: |
-        gem install bundler:2.1.4
-        bundle config path vendor/bundle
-    - name: Cache gems
-      uses: actions/cache@v1
-      with:
-        path: vendor/bundle
-        key: ${{ runner.os }}-gems-${{ hashFiles('**/Gemfile.lock') }}
-        restore-keys: |
-          ${{ runner.os }}-gems-
-    - name: Install gems
-      if: steps.cache.outputs.cache-hit != 'true'
-      run: bundle install --jobs 4 --retry 3
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
     - name: Build and test with Rake/Rubocop
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}