support ruby version is >= 3.1

Author: kuboon

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.6', '2.7', '3.0']
+        ruby-version: ['3.1', '3.2', '3.3', '3.4']
 
     steps:
     - uses: actions/checkout@v4