Don't push to NuGet from AppVeyor
Don't push to NuGet from AppVeyor

We can potentially turn the AppVeyor integration down entirely later
on, but at least for now let's make sure packages are pushed manually.

Signed-off-by: Jon Skeet <8a9602d66334021c18cbf0bdb2fa15f4cb6de9df@google.com>

cloudevents/sdk-csharp,cloudevents/sdk-csharp