Fix Docker login action with explicit registry

Author: Alex Hoffmann

.github/workflows/docker-build.yml

@@ -31,6 +31,7 @@ jobs:
       - name: Log in to Docker Hub
         uses: docker/login-action@v3
         with:
+          registry: docker.io
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}