Bump actions/checkout from 3 to 4 (#44)

Author: dependabot[bot]

.github/workflows/ruby.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Ruby 2.6
       uses: ruby/setup-ruby@v1
       with: