Bump version to 5.13.0

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.12.0...34ddecb09ae2c93485111d8f034f0c3a9a2b948f

• Release notes:

### New scenarios and scenario updates

- !456 Add elasticsearch version variable to be read from environment variable
- !457 Adds a component to test the release instance

• 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.