avoid creating unnecessary headers instance

[anonrig]

Let's make sure that we don't copy all of the headers, just to mutate it.

Part of https://github.com/opennextjs/opennextjs-aws/pull/1002

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Latest commit: a955067726d41f522c48de193c7026d7b4ab0577

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

This PR includes changesets to release 2 packages

Name	Type
@opennextjs/aws	Patch
app-pages-router	Patch

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