fix: RUST_TOOLCHAIN need to be inside of from block (#840)

Dockerfile

@@ -5,11 +5,12 @@ ARG CUDA_VERSION=11.7.1
 ARG BASE_CUDA_DEV_CONTAINER=nvidia/cuda:${CUDA_VERSION}-devel-ubuntu${UBUNTU_VERSION}
 # Target the CUDA runtime image
 ARG BASE_CUDA_RUN_CONTAINER=nvidia/cuda:${CUDA_VERSION}-runtime-ubuntu${UBUNTU_VERSION}
-# Rust toolchain version
-ARG RUST_TOOLCHAIN stable
 
 FROM ${BASE_CUDA_DEV_CONTAINER} as build
 
+# Rust toolchain version
+ARG RUST_TOOLCHAIN stable
+
 ENV DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \