Bump govuk-frontend from 5.5.0 to 5.6.0

Bumps [govuk-frontend](https://github.com/alphagov/govuk-frontend) from 5.5.0 to 5.6.0.
- [Release notes](https://github.com/alphagov/govuk-frontend/releases)
- [Changelog](https://github.com/alphagov/govuk-frontend/blob/main/CHANGELOG.md)
- [Commits](alphagov/govuk-frontend@v5.5.0...v5.6.0)

---
updated-dependencies:
- dependency-name: govuk-frontend
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>