chore: update CI ruby versions

Author: Mattia Roccoberton

.github/workflows/specs_rails70.yml

@@ -15,7 +15,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: ['2.7', '3.0']
+        ruby: ['3.0', '3.1', '3.2']
         gemfile: ['rails70_activeadmin']
 
     env: