Non-SSO and SSO accounts can sometimes fail to link

Created by: slimsag

A user at https://app.hubspot.com/contacts/2762526/company/557476528/ reported they were able to sign into Sourcegraph via GitHub but when searching got obscure github-proxy: 401 errors.

I believe this was due to the user previously having signed in via Sourcegraph's builtin authentication, and then subsequently via GitHub SSO. Strangely, the user's email address on GitHub (not public) was verified and matched their verified email address on Sourcegraph as well.

To resolve the issue, we had the site admin delete the user's account and the user sign in again via GitHub SSO.

This is a tracking issue in case we see any more instances of this.