errors.Is does not work properly with NCError

std library function errors.Is does not work when error is created with NCError 

create error:
```go
ErrAzureEABillingConfigNotFound      = errors.New("Azure EA billing config not found", nil)
```

error check fails:
```go
if errors.Is(err, billingcfg.ErrAzureEABillingConfigNotFound) {
    c.JSON(http.StatusNotFound, internalErrorToResponse(err))
    
    return
}
```