Strange result with `set-cookie` header of `undici.fetch`

Bug Description

Result of set-cookie, Set-cookie, and sEt-CoOkIe header value should be same, but undici.fetch has different result.

Reproducible By

const { fetch } = require('undici');

const response = await fetch('https://maple.gg');

console.log(response.headers); // has set-cookie
console.log(response.headers.get('set-cookie')); // undefined
console.log(response.headers.get('Set-cookie')); // some cookie key and value
console.log(response.headers.get('sEt-CoOkIe')); // some cookie key and value

Expected Behavior

I think all result of get should be same.

Logs & Screenshots

Environment

Ubuntu 20.04 Node v16.14.2

Additional context

[KhafraDev]

set-cookie is a forbidden header-name so it should be removed entirely (this is similar behavior with browser)

however getting a non-existent header should return null, not undefined.

edit: fixed both bugs and will make a PR soon.

[KhafraDev]

Reverted? Probably not. However I’m willing to make a PR once a decision has been made on how to handle cookies in undici/node.