fix: allow await in svelte boundary without pending

[yuki0418]

Fix: #16856

I referred #16817, but to sure if it is correct.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 9a91267

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

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

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[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16857

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-16857-svelte.vercel.app/

[dummdidumm]

thank you!