docs: fix two element_invalid_self_closing_tag warning in example

[adiguba]

Just two small corrections in example that generate the element_invalid_self_closing_tag warning.

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[changeset-bot]

⚠️ No Changeset found

Latest commit: 26dc3e2

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15324-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15324

[paoloricciuti]

Thanks!