TypeError: cookies is not iterable

[Vextil]

Describe the bug

After updating kit from 1.5.5 to 1.7.1 I'm getting the following error on every request:

TypeError: cookies is not iterable
    at Headers.get [headers map sorted] (/project/app/node_modules/undici/lib/fetch/headers.js:430:29)
    at /project/app/node_modules/undici/lib/fetch/headers.js:476:21
    at Headers Iterator.next (/project/app/node_modules/undici/lib/fetch/util.js:731:22)
    at Module.serialize_data (/node_modules/@sveltejs/kit/src/runtime/server/page/serialize_data.js:55:24)
    at eval (/node_modules/@sveltejs/kit/src/runtime/server/page/render.js:367:27)
    at Array.map (<anonymous>)
    at Module.render_response (/node_modules/@sveltejs/kit/src/runtime/server/page/render.js:366:5)
    at async Module.render_page (/node_modules/@sveltejs/kit/src/runtime/server/page/index.js:306:10)
    at async resolve (/node_modules/@sveltejs/kit/src/runtime/server/respond.js:371:17)
    at async Module.respond (/node_modules/@sveltejs/kit/src/runtime/server/respond.js:242:20)

Reproduction

Happens when making a server-side fetch to an endpoint that returns a Set-Cookie header.

Seems to be an issue with the new undici version:
nodejs/undici#1935

Fixed here, but no release yet:
nodejs/undici#1936

Logs

No response

System Info

System:
    OS: Linux 5.15 Ubuntu 22.04.1 LTS 22.04.1 LTS (Jammy Jellyfish)
    CPU: (8) x64 AMD Ryzen 5 5600G with Radeon Graphics
    Memory: 2.42 GB / 5.95 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 16.17.0 - /usr/local/bin/node
    npm: 8.15.0 - /usr/local/bin/npm
  npmPackages:
    @sveltejs/adapter-auto: ^1.0.0 => 1.0.3 
    @sveltejs/adapter-cloudflare: ^2.0.1 => 2.0.2 
    @sveltejs/adapter-node: ^1.1.8 => 1.2.0 
    @sveltejs/kit: ^1.7.1 => 1.7.1 
    svelte: ^3.55.0 => 3.55.1 
    vite: ^4.1.0 => 4.1.2

Severity

blocking an upgrade

Additional Information

Probably nothing we can do other than waiting for a new undici version. Rollback not recommended because of security vulnerabilities.
Publishing the issue anyway so if anyone else runs into the same issue they can find this.

[Vextil]

Fixed on #9106
Latest 1.8.3 version of SvelteKit is working fine.