Fix global is not defined on vercel edge

[juanvillacortac]

Closes #6424

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🦋 Changeset detected

Latest commit: 41d9c8d

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

This PR includes changesets to release 2 packages

Name	Type
@sveltejs/adapter-vercel	Patch
@sveltejs/adapter-auto	Patch

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[Rich-Harris]

Thanks — I don't love adding hacks like this to work around bugs in libraries, but since this bug is probably quite widespread we'll make an exception.