fix(ci): remove --api-key to use nuget.org Trusted Publishing (OIDC)

- The --api-key parameter triggers API key auth, not OIDC
- OIDC requires id-token: write (already added) and NO api-key
- nuget.org Trusted Publisher is configured for this repo

Co-Authored-By: Claude <noreply@anthropic.com>

Author: JusterZhu

.github/workflows/dotnet-ci.yaml

@@ -63,7 +63,6 @@ jobs:
           foreach ($nupkg in $nupkgs) {
             Write-Host "推送 $($nupkg.Name)..."
             dotnet nuget push $nupkg.FullName `
-              --api-key azure `
               --source https://api.nuget.org/v3/index.json `
               --skip-duplicate
           }