Setup correct usage of ruby versions to GHA matrix

Author: tiinapennala

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: [2.6, 2.7, 3.0, 3.4]
+        ruby: ['2.6', '2.7', '3.0', '3.4']
         gemfile:
           - Gemfile
           - Gemfile.rails-5.0.x