Use correct syntax for environment variable

[ThomasPiskol]

Fixes the upload issue due to missing API key because of wrong syntax.

[ThomasPiskol]

@am11 That should fix the issue with token which you have faced.

[am11]

Thank you! 🎉

[am11]

Ah, it failed again: https://github.com/package-url/packageurl-dotnet/runs/5346177918
Perhaps the key which was added in repository secrets is incorrect?

[ThomasPiskol]

Ok, it seems that this time it's not issue with token or the script.

There's already an existing NuGet package with the same ID available on nuget.org: https://www.nuget.org/packages/PackageUrl/

Due to the existing package we cannot publish our own package.
So we can either ask the owner of the existing package to remove his version and transfer the ownership of this package ID to us. But I'm not sure if it's possible to transfer the ownership of an existing Package ID on NuGet.org at all.

The other option I see is to change our package ID (currently PackageUrl) to something else (e.g. packageurl-dotnet)

[ThomasPiskol]

@am11 I've created an issue: #12 let's continue the discussion there.