ci: add ruby-4.0

Author: yoshoku

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '3.2', '3.3', '3.4' ]
+        ruby: [ '3.2', '3.3', '3.4', '4.0' ]
     steps:
       - uses: actions/checkout@v6
       - name: Install BLAS and LAPACK