Hello Guix!

Just used `guix refresh enchive` and received this email from github:

> On February 12th, 2020 at 09:19 (UTC) your personal access token (guix refresh) using GNU Guile was used as part of a query parameter to access an endpoint through the GitHub API:

> https://api.github.com/repositories/83831780/releases

> Please use the Authorization HTTP header instead, as using the `access_token` query parameter is deprecated and will be removed July 1st, 2020.

> Depending on your API usage, we'll be sending you this email reminder once every 3 days for each token and User-Agent used in API calls made on your behalf.
> Just one URL that was accessed with a token and User-Agent combination will be listed in the email reminder, not all.

> Visit https://developer.github.com/changes/2019-11-05-deprecated-passwords-and-authorizations-api/#authenticating-using-query-parameters for more information.

> Thanks,
> The GitHub Team

I think the code responsible is import/github.scm:159

A tentative fix is attached, but I'm not sure how to test it


Thanks, Nicolò