CI against Ruby 3.3

ruby/setup-ruby#553 has been merged.

Author: koic

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu]
-        ruby: ['2.7', '3.0', '3.1', '3.2', 'head']
+        ruby: ['2.7', '3.0', '3.1', '3.2', '3.3', 'head']
 
     steps:
       - name: checkout