[fix] Adapter netlify: don't set the request body on get/head requests

[JeanJPNM]

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Fixes #3438 by checking the request method before setting the body of the request object.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6b779da

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/adapter-netlify	Patch

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[Rich-Harris]

thanks!