login to docker hub before publishing

Signed-off-by: Avi Deitcher <avi@deitcher.net>

.github/workflows/publish.yaml

@@ -53,6 +53,11 @@ jobs:
         key: ${{ runner.os }}-linuxkit-${{ github.sha }}
         restore-keys: |
           ${{ runner.os }}-linuxkit-
+    - name: Login to Docker Hub
+      uses: docker/login-action@v2
+      with:
+        username: ${{ secrets.DOCKERHUB_USERNAME }}
+        password: ${{ secrets.DOCKERHUB_TOKEN }}
     - name: Publish Packages
       # this should only push changed ones:
       #  - unchanged: already in the registry
@@ -60,4 +65,3 @@ jobs:
       # Skip s390x as emulation is unreliable
       run: |
         make OPTIONS="--skip-platforms linux/s390x" -C pkg push PUSHOPTIONS="--nobuild"
-