Add Ruby 4.0 to the testing matrix in GitHub Actions workflow

Author: kojix2

.github/workflows/test.yml

@@ -15,7 +15,7 @@ jobs:
           - macos-15-intel
           - macos-latest
           - windows-latest
-        ruby: ["2.7", "3.2", "3.3", "3.4"]
+        ruby: ["2.7", "3.2", "3.3", "3.4", "4.0"]
     runs-on: ${{ matrix.runner }}
     steps:
       - uses: actions/checkout@v6