Add Ruby 4 to CI (#1659)

Author: larouxn

.github/workflows/ci.yml

@@ -43,7 +43,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '3.0', '3.1', '3.2', '3.3', '3.4' ]
+        ruby: [ '3.0', '3.1', '3.2', '3.3', '3.4', '4.0' ]
         experimental: [false]
         include:
           - ruby: head