add 3.4 to CI

.github/workflows/ruby.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ["3.3"]
+        ruby: ["3.3", "3.4"]
     steps:
       - uses: actions/checkout@v4
       - name: Set up Ruby