Users of MR Pipelines with private GitLab Runners of version 11.8 or older must upgrade to 11.9 or newer, or you will run into the issue described in gitlab-ee#11122, where you receive the error message
Your runner is outdated, please upgrade your runner. You can upgrade by following the instructions on the Runner installation guide. Users of GitLab's shared Runner fleet are not impacted by this issue.
Please let us know in the comments if you run into any issues.