GitHub Actions: publish :latest and :latest-debug also to GitHub Container Registry

- DockerHub is ok, but will be ratelimited soon, so this could be a nice alternative

.github/workflows/master-latest.yaml

@@ -26,12 +26,19 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-buildxarch-
 
-      - name: Login to DockerHub
+      - name: Docker Login to DockerHub
         uses: docker/login-action@v1
         with:
           username: ${{ secrets.DOCKER_HUB_USERNAME }}
           password: ${{ secrets.DOCKER_HUB_ACCESS_TOKEN }}
 
+      - name: Docker Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ secrets.DOCKER_GITHUB_USERNAME }}
+          password: ${{ secrets.DOCKER_GITHUB_PAT }}
+
       # the arm64 is of course much slower due to qemu, so build and push amd64 **first**
       # due to the way manifests work, the gap between this and the complete push below
       #  could result in pull failures or inconsistencies for arm64, such is life.
@@ -46,7 +53,7 @@ jobs:
           context: .
           file: ./Dockerfile
           platforms: linux/amd64
-          tags: rpardini/docker-registry-proxy:latest
+          tags: rpardini/docker-registry-proxy:latest,ghcr.io/rpardini/docker-registry-proxy:latest
           push: true
           cache-from: type=local,src=/tmp/.buildx-cache/release
           cache-to: type=local,mode=max,dest=/tmp/.buildx-cache/release
@@ -61,7 +68,7 @@ jobs:
           context: .
           file: ./Dockerfile
           platforms: linux/amd64
-          tags: rpardini/docker-registry-proxy:latest-debug
+          tags: rpardini/docker-registry-proxy:latest-debug,ghcr.io/rpardini/docker-registry-proxy:latest-debug
           push: true
           cache-from: type=local,src=/tmp/.buildx-cache/debug
           cache-to: type=local,mode=max,dest=/tmp/.buildx-cache/debug