Bump version to 5.4.3

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.4.2...d1378aa2ac536508c9188cf6e49749de4283aecd

• Release notes:

### Other changes (CI, backstage)

- !427 Handle reporter exceptions.

• 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.