Bump version to 7.26.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v7.25.1...d700245624972022680a02c2a7621fc7d62b2a15

• Release notes:

### Other changes (CI, backstage)

- !908 Add screenshots to failure issues

• 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.