Fix buildx multiarch

.github/workflows/docker.yml

@@ -27,6 +27,7 @@ jobs:
       - name: set up qemu
         uses: docker/setup-qemu-action@v1
       - name: set up buildx
+        id: docker_buildx
         uses: docker/setup-buildx-action@v1
       - name: log in to ghcr
         uses: docker/login-action@v1
@@ -37,7 +38,9 @@ jobs:
       - name: build and push
         uses: docker/build-push-action@v2
         with:
+          builder: ${{ steps.docker_buildx.outputs.name }}
+          platforms: linux/amd64, linux/arm64
           push: true
           tags: ghcr.io/lus/pasty:${{ env.TAG }}
           build-args:
-            PASTY_VERSION=${{ env.BRANCH }}-${{ env.COMMIT_HASH }}
+            PASTY_VERSION=${{ env.BRANCH }}-${{ env.COMMIT_HASH }}