Enable new typography scale

[DavidBiddle]

What problem does this pull request solve?

Trello card: https://trello.com/c/O48UNuIf/2364-switch-to-new-type-scale-for-admin

Switches on the new govuk-frontend type scale.

Things to consider when reviewing

• Ensure that you consider the wider context.
• Does it work when run on your machine?
• Is it clear what the code is doing?
• Do the commit messages explain why the changes were made?
• Are there all the unit tests needed?
• Do the end to end tests need updating before these changes will pass?
• Has all relevant documentation been updated?

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

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[thomasiles]

Looks good on the review app ⚖️