use multiple runners for the multi-arch build

.woodpecker/image.yml

@@ -1,15 +0,0 @@
-when:
-  - event: push
-    branch: "**"
-matrix:
-  platform:
-    - linux/amd64
-    - linux/arm64
-labels:
-  platform: ${platform}
-steps:
-  - name: build
-    image: woodpeckerci/plugin-docker-buildx
-    settings:
-      repo: brosner.dev/brosner/teufa
-      tag: wpp-${platform}