CI: Unpin ci-linux and use Rust 1.66.1 (paritytech#13134)

Author: rcny

.gitlab-ci.yml

@@ -48,7 +48,7 @@ variables:
   CARGO_INCREMENTAL:               0
   DOCKER_OS:                       "debian:stretch"
   ARCH:                            "x86_64"
-  CI_IMAGE:                        "paritytech/ci-linux@sha256:9140bc3c843a8b12a3bcf6f5886346536092795bbadfd7f1836362cb28dfcc71"
+  CI_IMAGE:                        "paritytech/ci-linux:production"
   BUILDAH_IMAGE:                   "quay.io/buildah/stable:v1.27"
   RUSTY_CACHIER_SINGLE_BRANCH:     master
   RUSTY_CACHIER_DONT_OPERATE_ON_MAIN_BRANCH: "true"