Bump version to 5.12.0

• Diff: v5.10.1...1ea430ec

• Release notes:

### New scenarios and scenario updates

- !451 Add a new Scenario and component for Jira.

• 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.