Update skunk workflow

Fix [this action](https://github.com/fastruby/skunk/actions/runs/4109939927/jobs/7092277419)

Author: JuanVqz

.github/workflows/skunk.yml

@@ -6,11 +6,12 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Setup Ruby
-        uses: actions/setup-ruby@v1
+        uses: ruby/setup-ruby@v1
         with:
           ruby-version: 2.6.x
+          bundler-cache: true
       - name: Run test suite with COVERAGE=true
         run: |
           gem install bundler