ci: Remove redundant rustup toolchain in Dockerfile-rust

Author: backkem

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Bug Fixes:
+
+- fix(docker): Use base image toolchain instead of reinstalling stable, which could pull in an unvalidated Rust version.
+
 ### Breaking:
 
 - breaking(domain) - service-version oriented `domain` commands have been moved under the `service domain` command. Versionless `domain-v1` commands have been moved to the `domain` command ([#1615](https://github.com/fastly/cli/pull/1615))

Dockerfile-rust

@@ -1,9 +1,8 @@
 FROM rust:latest
 LABEL maintainer="Fastly OSS <oss@fastly.com>"
 
-ENV RUST_TOOLCHAIN=stable
-RUN rustup toolchain install ${RUST_TOOLCHAIN} \
-  && rustup target add wasm32-wasip1 --toolchain ${RUST_TOOLCHAIN} \
+ENV RUSTUP_TOOLCHAIN=$RUST_VERSION
+RUN rustup target add wasm32-wasip1 \
   && apt-get update && apt-get install -y curl jq && apt-get -y clean && rm -rf /var/lib/apt/lists/* \
   && cargo install wasm-tools --locked \
   && export FASTLY_CLI_VERSION=$(curl -s https://api.github.com/repos/fastly/cli/releases/latest | jq -r .tag_name | cut -d 'v' -f 2) \