CI: permission issues when you're an admin : The requested URL returned error: 403

Summary

If you start a pipeline in a project you're not member (so you're an admin), CI results in 403 error.

Steps to reproduce

As an administrator, and not a member of the project, start a pipeline.

Example Project

It works on any project

What is the current bug behavior?

It produces a 403 error during project code download.

What is the expected correct behavior?

It shouldn't fail as I'm an admin. So I should be allowed to run the pipeline and so the runner should be allowed to get the code.

Relevant logs and/or screenshots

remote: You are not allowed to download code from this project.
fatal: unable to access 'http://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@git.example.com/toto/example.git/': The requested URL returned error: 403
ERROR: Job failed: exit code 1

Results of GitLab environment info

Using GitLab 10.6.0

Maybe related to #39469 (moved)