Update version to 8.4.1

Diff

https://gitlab.com/gitlab-org/gitlab-qa/compare/v8.4.0...b4560f9ac2bf8f9f2c3aac452e20c8b796e2259a

Release notes:

Fixes

• Fix pipeline name detection (!1032 - merged)

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.