Fix heading styling on alternative ID page

[libuk]

JIRA

Screenshots of UI changes

Before

After

Release checklist

As part of our continuous deployment strategy we must ensure that this work is
ready to be released at any point. Before merging to main we must first
confirm:

Pre merge checklist

• Are any changes required to the e2e tests?
• If you've added a new route, have you added a new
  auditEvent? (see server/routes/apply.ts for examples)
• Are there environment variables or other infrastructure configuration which needs to be included in this release?
• Are there any data migrations required. Automatic or manual?
• Does this rely on changes being deployed to the CAS API?

Post merge

Once we've merged it will be auto-deployed to the dev environment.

[patrickjfl]

Nice job!