Update GitHub Actions checkout to v4

Upgraded the GitHub Actions checkout step from v2 to v4 in the docker-build workflow. This change ensures compatibility with the latest features and improvements in the actions/checkout repository.

.github/workflows/docker-build.yml

@@ -61,7 +61,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v2