Update build.yml

Author: partouf

.github/workflows/build.yml

@@ -34,6 +34,7 @@ jobs:
       id: hub_build
       uses: docker/build-push-action@v5
       with:
+        platforms: linux/amd64
         push: ${{ github.ref == 'refs/heads/main' && 'true' || 'false' }}
         tags: compilerexplorer/${{ matrix.image }}-builder:latest
         cache-from: type=registry,ref=compilerexplorer/${{ matrix.image }}-builder:latest