repo-updater: Prevent HTTPS redirect in github source tests

Created by: keegancsmith

It seems when we redirected we wouldn't set the Authorization header, leading to our requests actually being unauthenticated. I noticed this problem when adding a test case which returned a large result set (1000+). The test was failing to record due to rate limits, since the requests were actually unauthenticated.

I chose to just make a specific wrapper for github-proxy since this is the only use of it, it will likely remain the only use of it, and making it generic is less clear / unneccessary given the previous points.

Test Plan: Removed authorization header scrubbing. Set GITHUB_ACCESS_TOKEN. Ran tests with update and noted the authorization header was not present for requests to api.github.com. Applied this change and run tests with update again. Authorization header was present.