Add Ruby 3.3 to CI matrix (#348)

Author: m-nakamura145

.github/workflows/tests.yml

@@ -22,6 +22,7 @@ jobs:
           - '3.0' # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
           - 3.1
           - 3.2
+          - 3.3
           - jruby
           - truffleruby
     steps: