use multiple runners for the multi-arch build

.gitea/workflows/ci.yml

@@ -94,7 +94,6 @@ jobs:
       - name: Setup docker buildx
         uses: docker/setup-buildx-action@v3
       - name: Build image
-        id: build
         uses: docker/build-push-action@v6
         with:
           tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
@@ -103,8 +102,3 @@ jobs:
           target: prod
           platforms: ${{ matrix.arch.platform }}
           outputs: type=image,push-by-digest=true,name-canonical=true,push=true
-      - name: Export digest
-        run: |
-          mkdir -p ${{ runner.temp }}/digests
-          digest="${{ steps.build.outputs.digest }}"
-          touch "${{ runner.temp }}/digests/${digest#sha256:}"