Bump version to 5.8.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.7.0...e5ada1abac123ef21147b5ce4613fd2f4eee232e

• Release notes:

### Other changes (CI, backstage)

- !441 Add Geo replication wait times to supported env vars
- !440 Skip orchestrated tests in the Praefect jobs

• 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.