fix: wait for commit promise instead of settled

[paoloricciuti]

Since we now fork every time, we should wait on the commit promise rather than settled (there are technically a couple of svelte versions where settled is there and works but not fork so maybe we could also wait for settled concurrently, but I'd say it's probably overkill).

Without this, #14800 is basically non-useful since settled resolves immediately if we invoke it after awaiting load_cache_fork😅

P.s. for some reason running the test locally I see a bunch of failing tests...but that's also true before the change so 🤷🏼

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🦋 Changeset detected

Latest commit: 346dce8

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

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@sveltejs/kit	Patch

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[Rich-Harris]

LGTM