GitHub provider doesn't support two-factor authentication

[maxkatz6]

Github providers doesn't support two-factory authentication.
Tested on 897fb96 master with Avalonia host.

[worldbeater]

A temporary solution is going to Settings > Developer settings > Personal access tokens > Generate new token and using that token instead of password. To fix that, we need to create a separate view model, TwoFactorAuthViewModel, and handle two-factor authentication there. Probably need to introduce some additional abstractions.