Update version to 8.9.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v8.8.0...6554ab78c7573f4d246e77b572c367bede94be1f

• Release notes:

### New scenarios and scenario updates

- !1023 <jz-enable-gitlab-pages> 

• 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:

  • Update the release notes for the newly created tag.