az sentinel alert-rule list command does not return the expected number of alert rules

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**Describe the bug**
`az sentinel alert-rule list` command does not return the expected number of alert rules. From the portal, we see that we have 181 alert rules enabled, but the az command only returns 143. This is true when using the Azure REST API directly as well.

**To Reproduce**
- see the number of alert-rules enabled from Microsoft Sentinel in the Azure portal.
- request the number of alert rules via the azure cli or via the Azure REST API:
```ps1
$url = "https://management.azure.com/subscriptions//resourceGroups//providers/Microsoft.OperationalInsights/workspaces//providers/Microsoft.SecurityInsights/alertRules?api-version=2020-01-01"
$method = "GET"
$token = Get-AzAccessToken -ResourceUrl "https://management.azure.com/"
$token = $token.Token
$headers = @{Authorization = "Bearer $token"}
$response = Invoke-RestMethod -Uri $url -Method $method -Headers $headers
$response.value.Count
```

**Expected behavior**
The number of alert-rules should be equal.