chore(deps): update actions/checkout action to v6 (#40)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
         ruby: [ '2.5', '2.6', '2.7', '3.0']
     name: Lint & Test with Ruby ${{ matrix.ruby }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}