Update version to 8.5.0

Diff:

https://gitlab.com/gitlab-org/gitlab-qa/compare/v8.4.2...57adc84be94c3ecf68fcadd995e7e089500ca32f

Release notes:

New scenarios

• Add Suggested Reviewer scenario (!1024 - merged)

Fixes

• Correctly pass docker cmd to ShellCommand (!1041 - merged)
• Fix mask_secrets in shell_command to Use Mutabl... (!1044 - merged)
• Use correct registry for qa image when running ... (!1046 - merged)

Other changes (CI, backstage)

• Extract generic shell command from docker command (!1031 - merged)
• Use rails commit sha as image tag for auto-depl... (!1042 - merged)
• Remove adding of devops::stage from results_rep... (!1045 - merged)

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.