NGINX.NGINXPLUS/stable/2022-08-01 - Nginx deployment Identity did not support `SystemAssigned`

When the swagger says support `SystemAssigned` but when create nginx deployment with SystemAssigned, API response with error.

related swagger: https://github.com/Azure/azure-rest-api-specs/blob/1d9c9c68844d2b5883621069d5bf0c958841782f/specification/nginx/resource-manager/NGINX.NGINXPLUS/stable/2022-08-01/swagger.json#L1033-L1039
error message:

```
{
"error": {
"code": "CannotSetResourceIdentity",
"message": "Resource type 'NGINX.NGINXPLUS/nginxDeployments' does not support creation of 'SystemAssigned' resource identity. The supported types are 'UserAssigned'."
}
}
```

Open specification/nginx/resource-manager/NGINX.NGINXPLUS/stable/2022-08-01/swagger.json at lines 1033-1039 and compare the declared identity support with the reported API error. Trace the relevant NGINX deployment identity definition and verify that the specification and service behavior agree about SystemAssigned support.

Written by the indexing model from the issue text.