test against ruby 3.3

Author: DannyBen

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     strategy:
-      matrix: { ruby: ['3.0', '3.1', '3.2', head] }
+      matrix: { ruby: ['3.0', '3.1', '3.2', '3.3'] }
 
     steps:
     - name: Checkout code