Bump version to 6.1.2

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v6.1.1...f244b39b94128e0b913e8ca1b05b00b8d5faa51a

• Release notes:

### Other changes (CI, backstage)

- !515 Revert "Temporarily switch back to reporting from XML".
- !520 Rename `status_issue` tag to `testcase`

• 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.