CI: permission issues when you're an admin : The requested URL returned error: 403
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### 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 gitlab-ce#39469
issue