Code-Quality.gitlab-ci.yml: automatically clean-up docker container

Adds the '--rm' option to 'docker run' in Code-Quality.gitlab-ci.yml
such that the code quality container is automatically cleaned up
after it has run.

Changelog: fixed

lib/gitlab/ci/templates/Jobs/Code-Quality.gitlab-ci.yml

@@ -27,7 +27,7 @@ code_quality:
       }
     - docker pull --quiet "$CODE_QUALITY_IMAGE"
     - |
-      docker run \
+      docker run --rm \
         $(propagate_env_vars \
           SOURCE_CODE \
           TIMEOUT_SECONDS \