C# Add support for authenticated nuget feeds

**Description of the issue**

This is using advanced mode with `build-mode: none` to take advantage of the "no build" csharp analyzers.

When using authenticated nuget feeds with `build-mode: none`, CodeQL will try and restore the packages, however there are multiple errors within the logs indicating that the feed failed due to 401 errors:

```
[2026-03-20 02:10:31] [build-stdout] Checking if NuGet feed 'https://my-artifactory-feed' is reachable...
[2026-03-20 02:10:31] [build-stdout] Querying NuGet feed 'https://my-artifactory-feed' failed in a timely manner. Not considering the feed for use. The reason for the failure: Response status code does not indicate success: 401.
```

Empieza por rastrear la ruta del modo avanzado para el análisis de C# con build-mode: none, centrándote en dónde se comprueban los feeds de NuGet y se restauran los paquetes. Determina cómo deben llegar las credenciales de los feeds autenticados a esa ruta; el trabajo estará terminado cuando se puedan usar feeds autenticados sin los fallos 401 indicados.

Escrito por el modelo de indexación a partir del texto del issue.