Bump govuk-content-schema-test-helpers from 1.5.0 to 1.6.0
Bump govuk-content-schema-test-helpers from 1.5.0 to 1.6.0

Bumps [govuk-content-schema-test-helpers](https://github.com/alphagov/govuk-content-schema-test-helpers) from 1.5.0 to 1.6.0.
- [Changelog](https://github.com/alphagov/govuk-content-schema-test-helpers/blob/master/CHANGELOG.md)
- [Commits](https://github.com/alphagov/govuk-content-schema-test-helpers/compare/v1.5.0...v1.6.0)
alphagov/content-tagger,alphagov/content-tagger,alphagov/content-tagger