Make CI build single-arch

Multi-arch builds cannot be done locally, with the
docker type.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Author: alexellis

.github/workflows/build.yaml

@@ -31,7 +31,7 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           outputs: "type=docker,push=false"
-          platforms: linux/amd64,linux/arm64
+          platforms: linux/amd64
           build-args: |
             Version=dev
             GitCommit=${{ github.sha }}