Reenable ARM build

Author: pmeulen

.github/workflows/build-ssp.container.yaml

@@ -32,7 +32,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: ./docker
-          platforms: linux/amd64
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: |
             ghcr.io/openconext/openconext-devssp/devssp:latest