fix ruby 2 workflow to use cache

Author: h0tw1r3

.github/workflows/ruby.yml

@@ -13,8 +13,7 @@ jobs:
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: '2.7'
+        bundler: '2.4.22'
+        bundler-cache: true
     - name: Build and test with Rake
-      run: |
-        gem install bundler -v 2.4.22
-        bundle install --jobs 4 --retry 3
-        bundle exec rake
+    - run: bundle exec rake