Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/docker-image.yml

@@ -11,6 +11,6 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
     - name: Build the Docker image
       run: docker build . --file Dockerfile --tag my-image-name:$(date +%s)