Add Ruby 3.3 to CI matrix (#337)

.github/workflows/test.yml

@@ -5,7 +5,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.7, '3.0', 3.1, 3.2, head]
+        ruby: [2.7, '3.0', 3.1, 3.2, 3.3, head]
         gemfile: [rubocop-next, rubocop-old]
     runs-on: ubuntu-latest
     env: # $BUNDLE_GEMFILE must be set at the job level, so it is set for all steps