Change Docker Hub username to use secrets

Author: 3nids

.github/workflows/build-docker-image.yml

@@ -26,7 +26,7 @@ jobs:
       - name: Login to Docker Hub
         uses: docker/login-action@v3
         with:
-          username: ${{ vars.DOCKERHUB_USERNAME }}
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       - uses: docker/build-push-action@v5