docker: Use specific msrv for stable toolchain.

Signed-off-by: Jason Volk <jason@zemos.net>

docker/bake.sh

@@ -59,6 +59,8 @@ docker_dir="$PWD/$BASEDIR"
 runner_name=$(echo $RUNNER_NAME | cut -d"." -f1)
 runner_num=$(echo $RUNNER_NAME | cut -d"." -f2)
 builder_name="${GITHUB_ACTOR:-owo}"
+toolchain_toml="$docker_dir/../rust-toolchain.toml"
+rust_msrv=$(grep "channel = " $toolchain_toml | cut -d'=' -f2 | sed 's/\s"\|"$//g')
 rocksdb_opt_level=3
 rocksdb_portable=1
 git_checkout="HEAD"