gitlab-org/gitlab-ci-multi-runner#1478 Fixed phpunit command in the official doc didn't work.

What does this MR do?

A php CI example of official doc doesn't work now.

See gitlab-org/gitlab-ci-multi-runner#1478 please.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

What are the relevant issue numbers?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together