Bump version to 5.13.4

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v5.13.3...f0bc41b2c81d9d20fc8fec4c19c8a27e8f85894c

• Release notes:

### Fixes

- !467 Don't skip pull by default.

### Doc changes

- !455 Update what_tests_can_be_run.md

### Other changes (CI, backstage)

- !468 Extract component base class.

• 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.