fix: Node 20.13 compat

[juliusmarminge]

Seems like something in Node 20.13 is broken with the spread operator on Headers:

Symbols aren't enumerable so they shouldn't show up after a spread, yet they are...

Anyways, this refactor makes it compat with this new behavior, be it intentional or unintentional from their side...

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Name	Status	Preview	Comments	Updated (UTC)
docs-uploadthing	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 16, 2024 11:20am

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🦋 Changeset detected

Latest commit: 668d35b28019e8b3b92e0a42578b061ea01ce41c

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

This PR includes changesets to release 7 packages

| Name | Type | | ------------------- | ----- | | uploadthing | Patch | | @uploadthing/shared | Patch | | @uploadthing/nuxt | Patch | | @uploadthing/react | Patch | | @uploadthing/solid | Patch | | @uploadthing/svelte | Patch | | @uploadthing/vue | Patch |

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[juliusmarminge]

Opened an issue on Undici: https://github.com/nodejs/undici/issues/3267