Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Docker meta
         id: docker_meta
         uses: crazy-max/ghaction-docker-meta@v1.12.0