Bump version to 7.6.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/-/compare/v7.5.0...471f674fb2c1f082019e661234bd57e7d347068b

• Release notes:

### New scenarios and scenario updates

- !706 Add Registry with TLS scenario

• 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.