Update dependency govuk-frontend to v6

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
govuk-frontend (source)	^5.14.0 → ^6.1.0

---

• If you want to rebase/retry this PR, check this box

[renovate]

⚠️ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
• the branch becomes conflicted, or
• you click the rebase/retry checkbox if found above, or
• you rename this PR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: package-lock.json

npm warn Unknown env config "store". This will stop working in the next major version of npm. See `npm help npmrc` for supported config options.
npm error code ERESOLVE
npm error ERESOLVE could not resolve
npm error
npm error While resolving: @ministryofjustice/frontend@8.0.1
npm error Found: govuk-frontend@6.1.0
npm error node_modules/govuk-frontend
npm error   govuk-frontend@"^6.1.0" from the root project
npm error
npm error Could not resolve dependency:
npm error peer govuk-frontend@"^5.11.2" from @ministryofjustice/frontend@8.0.1
npm error node_modules/@ministryofjustice/frontend
npm error   @ministryofjustice/frontend@"^8.0.1" from the root project
npm error
npm error Conflicting peer dependency: govuk-frontend@5.14.0
npm error node_modules/govuk-frontend
npm error   peer govuk-frontend@"^5.11.2" from @ministryofjustice/frontend@8.0.1
npm error   node_modules/@ministryofjustice/frontend
npm error     @ministryofjustice/frontend@"^8.0.1" from the root project
npm error
npm error Fix the upstream dependency conflict, or retry this command with --force or --legacy-peer-deps to accept an incorrect (and potentially broken) dependency resolution.
npm error
npm error
npm error For a full report see:
npm error /runner/cache/others/npm/_logs/2026-03-13T13_08_58_796Z-eresolve-report.txt
npm error A complete log of this run can be found in: /runner/cache/others/npm/_logs/2026-03-13T13_08_58_796Z-debug-0.log