fix: correct link in types documentation

[KTibow]

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Someone in the Discord reported that there's a direct link to the vercel sveltekit docs instead of kit.svelte.dev for the typing for Action. This PR changes it to kit.svelte.dev.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 36da4ce

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[benmccann]

I added a changeset since the types will need to be republished