該当するコード
credential = GoogleCredential.FromStream(credentialStream).CreateScoped(Scopes);
var appendResponse = await appendRequest.ExecuteAsync();
解決策
link.xmlを書く
<linker>
<assembly fullname="Google.Apis.Auth" preserve="all"/>
<assembly fullname="Google.Apis" preserve="all"/>
<assembly fullname="Google.Apis.Core" preserve="all"/>