Use parent request headers in server-side fetch

[RaeesBhatti]

Fixes: #696

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🦋 Changeset detected

Latest commit: 976c62e

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

This PR includes changesets to release 1 package

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@sveltejs/kit	Patch

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[Rich-Harris]

Thank you — closing in favour of #3631, which is more current