Add Ruby 4.0 to CI

Author: jeremyevans

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ 3.4, 3.3, 3.2, 3.1, head ]
+        ruby: [ "4.0", 3.4, 3.3, 3.2, 3.1, head ]
     runs-on: ubuntu-24.04
     steps:
     - uses: actions/checkout@v6