ci: pass NuGet/login OIDC api key to dotnet nuget push

The previous run got past authentication (NuGet/login@v1 exchanged the
GitHub OIDC token for a short-lived NuGet.org API key) but then
`dotnet nuget push` had no way to use that key and got 401:

    No API Key was provided and no API Key could be found for
    'https://www.nuget.org/api/v2/package'
    error: Response status code does not indicate success: 401

NuGet/login@v1 exposes the key via outputs.NUGET_API_KEY. Give the auth
step an `id`, plumb the output through an env var, and pass it to
`dotnet nuget push --api-key`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ANcpLua

.github/workflows/nuget-publish.yml

@@ -82,14 +82,18 @@ jobs:
         run: dotnet pack CreatePdf.NET/CreatePdf.NET.csproj --configuration Release --no-build --output ./nupkg -p:GeneratePackageOnBuild=false
 
       - name: Authenticate with NuGet
+        id: nuget-auth
         uses: NuGet/login@v1
         if: github.event_name == 'release' || github.event_name == 'workflow_dispatch'
         with:
           user: ANcpLua
 
       - name: Publish packages to NuGet.org
         if: github.event_name == 'release' || github.event_name == 'workflow_dispatch'
+        env:
+          NUGET_API_KEY: ${{ steps.nuget-auth.outputs.NUGET_API_KEY }}
         run: |
           dotnet nuget push ./nupkg/*.nupkg \
             --source https://api.nuget.org/v3/index.json \
+            --api-key "$NUGET_API_KEY" \
             --skip-duplicate