Bump version to 8.6.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v8.5.0...dd662edb30547107d29a61bcc2c0ad154643002b

• Release notes:

### New scenarios and scenario updates

- !1052 Remove deprecated scenarios and components

### Other changes (CI, backstage)

- !1043 Assign DRI to failure issues

• 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.