Updated checkout action [skip ci]

Author: ankane

.github/workflows/build.yml

@@ -4,7 +4,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: "4.0"