Add Ruby 4.0 to CI matrix

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MatheusRich

.github/workflows/main.yml

@@ -13,7 +13,7 @@ jobs:
     name: Ruby ${{ matrix.ruby }} / Rails ${{ matrix.rails }}
     strategy:
       matrix:
-        ruby: [ '3.2', '3.3', '3.4' ]
+        ruby: [ '3.2', '3.3', '3.4', '4.0' ]
         rails: [ '7.x', '8.x' ]
     steps:
       - uses: actions/checkout@v4