One Issue for Az.DeploymentManager

## Description

Install the 'Az.DeploymentManager' module and test the Cmdlet 'Get-AzDeploymentManagerArtifactSource'.But the error message shows that the service failed when deserializing the response.

## Steps to reproduce

```powershell
Get-AzDeploymentManagerArtifactSource -ResourceGroupName 'testResourceGroupName'

```

## Environment data

```
Name Value
---- -----
PSVersion 7.1.0-preview.1
PSEdition Core
GitCommitId 7.1.0-preview.1
OS Microsoft Windows 10.0.19042
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
```

## Module versions

```powershell
ModuleType Version PreRelease Name PSEdition ExportedCommands
---------- ------- ---------- ---- --------- ----------------
Script 1.1.0 Az.DeploymentManager Core,Desk {Get-AzDeploymentManagerArtifactSource,…

```

## Error output

```
Newtonsoft.Json.JsonSerializationException: Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.IList`1[Microsoft.Azure.Management.DeploymentManager.Models.ArtifactSource]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly.
```