Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -8,6 +8,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5.0.0
+        uses: actions/checkout@v6.0.1
       - name: Run ShellCheck
         uses: ludeeus/action-shellcheck@1.1.0