The permissions for running CI will be restricted to external
contributors. It will only work for projects that use "detached MR
pipelines" ([1]).

Note that for it to actually work, a member with permission might have
to go to the "pipeline" tab of the merge request and click "run
pipeline". But this snippet is necessary for that.

[1] https://docs.gitlab.com/ee/ci/pipelines/merge_request_pipelines.html

freedesktop/freedesktop#540