Get-AzRoleAssignment returns Authorization_RequestDenied; whereas New-AzRoleAssignment and Remove-AzRoleAssignment works

# Description
This is similar to https://github.com/Azure/azure-powershell/issues/10550 possibly. I am using a service principal to manage IAM access to azure resources for which that service account is the owner.

Get-AzRoleAssignment returns Authorization_RequestDenied; whereas New-AzRoleAssignment and Remove-AzRoleAssignment work perfectly. The expected behavior is that this service principal can read and write azure AD accounts on applications it owns; but it seems it can only write.

The service principal account has the following access:

Azure Active Directory Graph (2) | Type  | Description  |Admin Consent Required   |  Status |  
-- | -- | -- | -- | -- | --
  | Application.ReadWrite.OwnedBy | Application | Manage apps that this app creates or owns | Yes | Granted for "omitted tenant name" |  
  | Directory.Read.All | Delegated | Read directory data | Yes | Granted for "omitted tenant name"

## Steps to reproduce

1. Create an Azure AD service principal, with the permissions above.
2. Create an azure resource, such as an azure storage account.
3. Grant the above service principal as an owner of the azure resource using the IAM blade in the azure portal

### New-AzRoleAssignment (works)
```powershell
New-AzRoleAssignment -Scope /subscriptions//providers/Microsoft.Storage/storageAccounts/ -ObjectId -RoleDefinitionName 'Reader'

```
### Get-AzRoleAssignment (fails)
```powershell
Get-AzRoleAssignment -Scope /subscriptions//providers/Microsoft.Storage/storageAccounts/

Get-AzRoleAssignment: Exception of type 'Microsoft.Rest.Azure.CloudException' was thrown.
```
## Environment data

```
Name Value
---- -----
PSVersion 7.0.3
PSEdition Core
GitCommitId 7.0.3
OS Darwin 19.6.0 Darwin Kernel Version 19.6.0: Thu Jun 18 20:49:00 PDT 2020; root:xnu-6153.141.1~1/RELEASE_X86_64
Platform Unix
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0

## Module versions

```powershell
Get-Module -ListAvailable | where name -eq Az

Directory: /Users//.local/share/powershell/Modules

ModuleType Version PreRelease Name PSEdition ExportedCommands
---------- ------- ---------- ---- --------- ----------------
Script 4.6.1 Az Core,Desk
```

## Debug output

```powershell
Body:
{
"odata.error": {
"code": "Authorization_RequestDenied",
"message": {
"lang": "en",
"value": "Insufficient privileges to complete the operation."
},
"requestId": "c6906c6a-13dd-4368-8c7d-c3383e75302e",
"date": "2020-09-02T22:48:46"
}
}

Get-AzRoleAssignment: Exception of type 'Microsoft.Rest.Azure.CloudException' was thrown.
```
Note, if more than this is needed please reach out and I will supply it privately.

## Error output

```
Resolve-AzError -Last
WARNING: Breaking changes in the cmdlet 'Resolve-AzError' :
WARNING: - The `Resolve-Error` alias will be removed in a future release. Please change any scripts that use this alias to use `Resolve-AzError` instead.

WARNING: NOTE : Go to https://aka.ms/azps-changewarnings for steps to suppress this breaking change warning, and other information on breaking changes in Azure PowerShell.

HistoryId: 449

RequestId :
Message : Exception of type 'Microsoft.Rest.Azure.CloudException' was thrown.
ServerMessage : : (System.Collections.Generic.List`1[Microsoft.Rest.Azure.CloudError])
ServerResponse : {Forbidden}
RequestMessage : {POST https://graph.windows.net//getObjectsByObjectIds?api-version=1.6}
InvocationInfo : {Get-AzRoleAssignment}
Line : Get-AzRoleAssignment -Scope /subscriptions//resourceGroups/datasvc-dev-rg/providers/Microsoft.Storage/storageAccounts/
Position : At line:1 char:1
+ Get-AzRoleAssignment -Scope /subscriptions …
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
StackTrace : at Microsoft.Azure.Graph.RBAC.ObjectsOperations.GetObjectsByObjectIdsWithHttpMessagesAsync(GetObjectsParameters parameters, Dictionary`2 customHeaders, CancellationToken cancellationToken)
at Microsoft.Azure.Graph.RBAC.ObjectsOperationsExtensions.GetObjectsByObjectIdsAsync(IObjectsOperations operations, GetObjectsParameters parameters, CancellationToken cancellationToken)
at Microsoft.Azure.Graph.RBAC.ObjectsOperationsExtensions.GetObjectsByObjectIds(IObjectsOperations operations, GetObjectsParameters parameters)
at Microsoft.Azure.Commands.ActiveDirectory.ActiveDirectoryClient.GetObjectsByObjectId(List`1 objectIds)
at Microsoft.Azure.Commands.Resources.Models.Authorization.AuthorizationClientExtensions.ToPSRoleAssignments(IEnumerable`1 assignments, IEnumerable`1 roleDefinitions, AuthorizationClient policyClient,
ActiveDirectoryClient activeDirectoryClient, Boolean excludeAssignmentsForDeletedPrincipals)
at Microsoft.Azure.Commands.Resources.Models.Authorization.AuthorizationClient.FilterRoleAssignments(FilterRoleAssignmentsOptions options, String currentSubscription, UInt64 first, UInt64 skip)
at Microsoft.Azure.Commands.Resources.GetAzureRoleAssignmentCommand.ExecuteCmdlet()
at Microsoft.WindowsAzure.Commands.Utilities.Common.AzurePSCmdlet.ProcessRecord()
HistoryId : 449

The Azure PowerShell team is listening, please let us know how we are doing: https://aka.ms/azpssurvey?Q_CHL=ERROR.
```