fix: wait a longer tick before checking slots

[dummdidumm]

It seems that browser resolve "await Promise.resolve()" extra fast (close to synchronous) so the DOM isn't actually updated further. This fixes an issue where web component slots don't appear when the script registering the web components is invoked before them being added to the DOM fixes #8997

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🦋 Changeset detected

Latest commit: 7ffa5f4

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[dummdidumm]

An alternative is to add some kind of mutation observer and adjust Svelte's fallback logic to swap out to fallback dynamically.