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

Author: renovate[bot]

.github/workflows/nextjs.yml

@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Detect package manager
         id: detect-package-manager
         run: |