gh: Manually push new base image

The docker driver of buildx does not support pushing
with the version of docker that is currently available
on github. So we have to do that manually.

.github/workflows/update-base.yaml

@@ -21,10 +21,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v1
-        with:
-          driver: docker
       - name: Docker login
         uses: docker/login-action@v1
         with:
@@ -34,12 +30,13 @@ jobs:
       - name: Calculate BASE image
         id: base
         run: .github/scripts/base-tag "${{ matrix.type }}"
-      - name: Build and push base image
+      - name: Build base image
         uses: docker/build-push-action@v2
         with:
           context: .
           file: .github/dockerfiles/Dockerfile.${{ steps.base.outputs.BASE_TYPE  }}
           pull: true
-          push: true
           build-args: BASE=${{ steps.base.outputs.BASE }}
           tags: docker.pkg.github.com/${{ github.repository }}/${{ matrix.type }}:latest
+      - name: Push base image
+        run: docker push docker.pkg.github.com/${{ github.repository }}/${{ matrix.type }}:latest