fix: add more extensive migration export regex

[eltigerchino]

fixes #8518

Adds a more extensive regex that checks for export let when a load function is present.

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🦋 Changeset detected

Latest commit: 019f4d8

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

This PR includes changesets to release 1 package

Name	Type
svelte-migrate	Patch

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[Rich-Harris]

thank you!