Add Ruby version 4.0 to CI workflow

Author: collimarco

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        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']
     steps:
     - uses: actions/checkout@v5
     - name: Set up Ruby