Resolve redirect_uri error when authentication with GitHub

[jnywong]

This is happening when trying to log in on both the staging & production websites, as well as a local version on the bestish branch.

I quickly tried locally investigating by changing SOCIALACCOUNT_LOGIN_ON_GET, ACCOUNT_DEFAULT_HTTP_PROTOCOL settings, but to no avail.

[jnywong]

The GitHub OAuth app lives under the 2i2c-org and the callback URL needed updating.