Remove Ruby 2.5 from GitHub Actions testing

Author: kojix2

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       matrix:
         os:   [ 'ubuntu', 'macos' ]
-        ruby: [ '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3' ]
+        ruby: [ '2.6', '2.7', '3.0', '3.1', '3.2', '3.3' ]
     steps:
       - uses: actions/checkout@v3
       - uses: ruby/setup-ruby@v1