Add Ruby 3.4 to CI

Author: kojix2

.github/workflows/ci.yml

@@ -6,8 +6,8 @@ jobs:
     runs-on: ${{ matrix.os }}-latest
     strategy:
       matrix:
-        os:   [ 'ubuntu', 'macos' ]
-        ruby: [ '2.6', '2.7', '3.0', '3.1', '3.2', '3.3' ]
+        os: ["ubuntu", "macos"]
+        ruby: ["2.6", "2.7", "3.0", "3.1", "3.2", "3.3", "3.4"]
     steps:
       - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1