fix: type link variants

[lihbr]

Resolves:

Description

Add missing types for link variants.

Checklist

• If my changes require tests, I added them.
• If my changes affect backward compatibility, it has been discussed.
• If my changes require an update to the CONTRIBUTING.md guide, I updated it.

Preview

How to QA ¹

• Checkout branch, install, and build
• npm link
• In a Slice Machine project: npm update @prismicio/client && npm link prismic-ts-codegen
• Add a link field with variants
• Check types

Footnotes

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