docs: fix some bad snippets

[Rich-Harris]

this, combined with an upgrade to the latest version of SvelteKit, should hopefully get the preview docs building again

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 8ca909c:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/8ca909cb527ff5c13fb7778aa39e197bec13963a

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16504

[changeset-bot]

⚠️ No Changeset found

Latest commit: 8ca909c

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16504-svelte.vercel.app/