ci: add 'NO_INSTALL' flag to ci/rust-version.sh (#6663)

ci/docker/env.sh

@@ -3,7 +3,7 @@
 ci_docker_env_sh_here="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 # shellcheck disable=SC1091
-source "${ci_docker_env_sh_here}/../rust-version.sh"
+NO_INSTALL=1 source "${ci_docker_env_sh_here}/../rust-version.sh"
 
 if [[ -z "${rust_stable}" || -z "${rust_nightly}" ]]; then
   echo "Error: rust_stable or rust_nightly is empty. Please check rust-version.sh." >&2

ci/rust-version.sh

@@ -37,6 +37,10 @@ export rust_stable="$stable_version"
 
 export rust_nightly=nightly-"$nightly_version"
 
+if [[ -n $NO_INSTALL ]]; then
+  return
+fi
+
 [[ -z $1 ]] || (
 
   rustup_install() {