update actions/checkout to v4 in GitHub workflow

Author: snickerjp

.github/workflows/docker-image.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Log in to Docker Hub
         uses: docker/login-action@v2.1.0