Bump govuk-frontend from 4.0.1 to 5.6.0 in /ntbs-service

Bumps [govuk-frontend](https://github.com/alphagov/govuk-frontend) from 4.0.1 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@v4.0.1...v5.6.0)

---
updated-dependencies:
- dependency-name: govuk-frontend
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

ntbs-service/package.json

@@ -25,7 +25,7 @@
  "es6-promise": "4.2.8",
  "file-loader": "6.2.0",
  "formdata-polyfill": "4.0.10",
- "govuk-frontend": "4.0.1",
+ "govuk-frontend": "5.6.0",
  "nhsuk-frontend": "6.1.0",
  "qs": "6.10.3",
  "sass": "1.49.9",