Add ruby v4 to test matrix

Author: unasuke

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-22.04
     strategy:
       matrix:
-        ruby: ["3.4", "3.3", "3.2", "3.1", "3.0", "2.7", "2.6"]
+        ruby: ["4.0", "3.4", "3.3", "3.2", "3.1", "3.0", "2.7", "2.6"]
     name: Ruby ${{ matrix.ruby }}
     steps:
       - uses: actions/checkout@v3