Only one cookie is being set when you have multiple Set-Cookie

[silentworks]

Describe the bug When using Netlify build we are only getting one cookie set when we have multiple Set-Cookie in the header. This is inconsistent with how the Remix dev server works and how the MDN docs say it should work.

To Reproduce Steps to reproduce the behavior:

1. Create a new remix app using the netlify template npx create-remix@latest --template netlify/remix-template
2. Edit the app/root.tsx file and add the following

   
   import type { MetaFunction } from "@remix-run/node";
   import {
   Links,
   LiveReload,
   Meta,
   Outlet,
   Scripts,
   ScrollRestoration,
   } from "@remix-run/react";
   import { json } from '@remix-run/node';

export const meta: MetaFunction = () => [{ charset: "utf-8", title: "New Remix App", viewport: "width=device-width,initial-scale=1", }];

export const loader = async () => { const ckHeaders = new Headers([ ["Set-Cookie", "lulu=meow; Max-Age=3600; Path=/; SameSite=Lax"], ["Set-Cookie", "booya=kasha; Max-Age=3600; Path=/; SameSite=Lax"], ]);

return json( {}, { headers: ckHeaders, } ); };

export default function App() { return (

); }

3. Run the build and start the netlify server using `npm run build && npm start`
4. When the browser opens check your cookie storage and you will notice only the second cookie was saved.

**Expected behavior**
Both cookies should be saved and not only the second one.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Desktop (please complete the following information):**
 - OS: MacOS
 - Browser Firefox
 - Version 2.2.0

**Additional context**
Add any other context about the problem here.

[ascorbic]

Thanks for the report. We've identified this as a bug in our new functions runtime so will prioritise a fix.

[ascorbic]

We have a fix ready. I'll update this ticket when it's rolled out

[silentworks]

Thank you so much for this @ascorbic.