Restore NuGet release publish secret

[peters]

Summary

• restore the previous NuGet.org publish secret reference after the beta publish failed at the NuGet push step with 403
• keep release packaging and upload behavior unchanged

Validation

• git diff --check
• Copilot review completed; the secret-name concern is intentionally accepted for this unblocker because the org-scoped key currently fails NuGet authorization

Release notes

• v1.0.0-beta.47 published release assets and crates.io packages, but Surge.NET was not accepted by NuGet. A replacement beta should be cut after this fix merges.

[Copilot]

Pull request overview

Restores the NuGet.org API key secret reference used by the GitHub Release workflow so Surge.NET publishing succeeds again, while keeping the rest of the release packaging/upload flow unchanged.

Changes:

• Update the dotnet nuget push step to use a different GitHub Actions secret for the NuGet.org API key.

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