Enable RUST_BACKTRACE for docker builds (#729)

They're failing on ARM atm, maybe this will help

.github/workflows/docker.yaml

@@ -57,6 +57,7 @@ jobs:
           platforms: linux/amd64,linux/arm64
           cache-from: type=gha
           cache-to: type=gha,mode=max
+          build-args: RUST_BACKTRACE=1
 
       - name: Image digest
         run: echo ${{ steps.docker_build.outputs.digest }}