Bump version to 5.13.0

• Diff: v5.12.0...34ddecb0

• 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.