Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/publish.yml

@@ -9,7 +9,7 @@ jobs:
   publish:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: '24.x'