Update ci.yml

Author: kojix2

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
         os:   [ 'ubuntu', 'macos', 'windows' ]
         ruby: [ '3.1', '3.2', '3.3' ]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}