Revert "github: temp disable ARM build."

This reverts commit 6a4a4da1bc.

.github/workflows/docker-build.yaml

@@ -29,10 +29,10 @@ jobs:
     steps:
       # https://github.com/docker/setup-qemu-action
       # https://github.com/docker/setup-buildx-action#with-qemu
-      #- name: Set up QEMU
-      #  uses: docker/setup-qemu-action@v1
-      #  with:
-      #    platforms: arm64
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+        with:
+          platforms: arm64
 
       # https://github.com/docker/setup-buildx-action
       - name: Set up Docker Buildx
@@ -80,8 +80,7 @@ jobs:
           tags: ${{ steps.metadata.outputs.tags }}
           labels: ${{ steps.metadata.outputs.labels }}
 
-            #platforms: linux/amd64,linux/arm64
-          platforms: linux/amd64
+          platforms: linux/amd64,linux/arm64
 
           # https://github.com/docker/build-push-action/blob/master/docs/advanced/cache.md#registry-cache
           # https://dev.to/pst418/speed-up-multi-stage-docker-builds-in-ci-cd-with-buildkit-s-registry-cache-11gi