Add Ruby 3.3 to build matrix

Author: jaynetics

.github/workflows/tests.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: [ '2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', 'ruby-head' ]
+        ruby: [ '2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', 'ruby-head' ]
 
     steps:
       - uses: actions/checkout@v4