'Cookie:' header dissapears on redirect

**Describe the bug**
Had a watch start failing recently due to being logged out. The only change was the page now redirects to a different page. I double checked the request in mitmproxy and the original request includes my cookie header, but the request following the redirect doesn't have the cookie header.

**Version**
v0.50.5

**How did you install?**
docker compose

**To Reproduce**

Steps to reproduce the behavior:
1. Create a watch
- Url: https://httpbin.org/redirect-to?url=https%3A%2F%2Fhttpbin.org/cookies
- Fetch method: 'Basic fast Plaintext/HTTP Client'
- Advanced options -> Request headers: `Cookie: examplecookie=3`

**Expected behavior**
Cookie header is sent with both the initial request and redirected request

I'd expect to see my cookies:


But instead they're missing:


**Screenshots**



**Additional context**
Dug in a bit and found that `requests` drops manually-set cookie headers when following a redirect in a session (https://github.com/psf/requests/blob/91a3eabd3dcc4d7f36dd8249e4777a90ef9b4305/src/requests/sessions.py#L235)
It doesn't look like they're interested in changing that behavior (https://github.com/psf/requests/issues/5714)