Fix publishing to MyGet

[martincostello]

Publishing NuGet packages to MyGet for prereleases versions has started failing.

Either the API token has expired, or some quota has been exceeded.

Something needs fixing so we can resume publishing.

[bkoelman]

In case it helps: I recently switched to feedz.io, after reading MyGet is mostly dead. xUnit is also using feedz.io; it may be worth trying.

[martincostello]

Yeah, I've used that myself too. Whatever the feed, I don't have access to the repo settings so I can't add any secrets, so I need the repo owner to fix it. I've contacted them via Slack, but otherwise just have to wait for them to address it.