Update version to 8.4.1

Diff

v8.4.0...b4560f9a

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.