Upgrade Ruby to 2.3.5

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3234

What does this MR do?

Update Ruby version to 2.3.5.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Part of gitlab-org/gitlab-ce#38040