Create better UI for incorrect/invalid GitHub token

[amanape]

What problem or use case are you trying to solve?
If the user enters an incorrect GitHub token through the "Connect to GitHub" modal, two toasts appear that don't clearly explain the issue.

Actually, the 500 status code error is due to a failed request to /api/github/repositories?sort=pushed&page=1&per_page=100 which should not execute at this time

Describe the UX of the solution you'd like
We previously re-opened the modal if the request failed, we should consider bringing this behaviour back. Instead of display an error toast here, re-open the modal and show an error message above or under the token input