Add Ruby v4.0 to CI

Author: collimarco

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-22.04, ubuntu-24.04]
-        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4']
+        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4', '4.0']
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v6