Publishing to Github Packages from Jenkins Using Cake

Question

I'm having an issue publishing to Github Packages from Jenkins using Cake.

The push task looks like this:

Task(nugetPushTask)
 .WithCriteria(() => isPublishBranch)
 .IsDependentOn(packTask)     
 .Does(() => {    

    foreach(var file in GetFiles(nugetFilesPath)) {
        DotNetNuGetPush(file, new DotNetNuGetPushSettings {
            ApiKey = "key_gdhsjgjhjkeykeykey",
            Source = "https://nuget.pkg.github.com/yourOrganizationOrAccount/index.json"
        });
    }

 }); 

Interestingly, I can successfully push the package with the following command:
dotnet nuget push nameofpackage.1.0.0.nupkg --source github --api-key key_gdhsjgjhjkeykeykey
using a shell prompt.

The error which I see in the build log for that step is:

An error occurred when executing task 'PublishGithub'.

System.Exception: Github Package Key Environment Variable is not set correctly.

at Submission#0.<>b__0_7(ICakeContext context)

at Cake.Core.CakeTaskBuilderExtensions.<>c__DisplayClass39_0.b__0(ICakeContext context) in C:\projects\cake\src\Cake.Core\CakeTaskBuilder.Execution.cs:line 81

at Cake.Core.CakeTask.Execute(ICakeContext context) in C:\projects\cake\src\Cake.Core\CakeTask.cs:line 119

at Cake.Core.DefaultExecutionStrategy.ExecuteAsync(CakeTask task, ICakeContext context) in C:\projects\cake\src\Cake.Core\DefaultExecutionStrategy.cs:line 69

at Cake.Core.CakeEngine.ExecuteTaskAsync(ICakeContext context, IExecutionStrategy strategy, Stopwatch stopWatch, CakeTask task, CakeReport report) in C:\projects\cake\src\Cake.Core\CakeEngine.cs:line 318

Can anyone advise how to get Cake to do what the CLI command is doing.

Thanks