Bump version to 5.7.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.6.1...45bc904582ddc198fcb90a9402957b411d465b04

• Release notes:

### Other changes (CI, backstage)

- !429 Update GitLab component with a new variable used for the formless login mechanism

• 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.