Bump version to 4.16.0

• Diff: v4.15.0...0e9baef7#

• Release notes:

### Fixes
- !348 If version matches an official tag, look for the same tag on dev

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/qa/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Create a tag for the new release version.

/label Quality ~backstage