Replace Ruby 2.7 with Ruby 3.3 in CI

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     name: build (${{ matrix.ruby }}
     strategy:
       matrix:
-        ruby: [ 3.2, 3.1, '3.0', 2.7, head ]
+        ruby: [ 3.3, 3.2, 3.1, '3.0', head ]
     runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v4