GitHub username can be invalid after a user changed it.

[pinterid]

Describe the bug
If a user changes his name on GitHub his profile can no longer be found by SNEK.

To Reproduce
Steps to reproduce the behavior:

1. Link a GitHub account to SNEK
2. Go to GitHub
3. Change your GitHub username
4. Got to SNEK
5. Login with your SNEK credentials
6. Wait for re-querying
7. See bug

Expected behavior
The username should be automatically updated using the GitHub access token.

Desktop (please complete the following information):

• Any

Smartphone (please complete the following information):

• Any

Additional context
Add any other context about the problem here.