Update Ruby version in GitHub Actions workflow from 2.4 to 2.7

Author: Cosima Radu

.github/workflows/rspec.yml

@@ -21,7 +21,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 2.4
+          ruby-version: 2.7
           bundler-cache: true
 
       - name: Run tests