Add `.nupkg` to GitHub releases as mirror

[o-l-a-v]

Summary of the new feature / enhancement

It'd be nice if the .nupkg published to PowerShell Gallery also could be added to each GitHub release, in case the PowerShell Gallery goes down and users needs PSResourceGet to install packages from other supported repositories:

• https://learn.microsoft.com/en-us/powershell/gallery/powershellget/supported-repositories

Proposed technical implementation details (optional)

• If in GitHub actions: https://github.com/softprops/action-gh-release