Update gitlab_git gem to 10.4.7

What does this MR do?

Update gitlab_git gem to 10.4.7

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

N/A

Why was this MR needed?

To take advantage of a couple of performance improvements introduced by the new version

What are the relevant issue numbers?

N/A

Screenshots (if relevant)

N/A

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