New-AzSqlDatabaseExport provides invalid storage key format for secrets received as parameter

### Description

I was trying to use storage key as secret string, but it is giving error
New-AzSqlDatabaseExport: D:\a\uda-mcs-sql-db-cloud\uda-mcs-sql-db-cloud\bkp.ps1:15
Line |
15 | … rtRequest = New-AzSqlDatabaseExport -ResourceGroupName $rgName -Serve …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| The ImportExport operation failed because of invalid storage key format.

### Issue script & Debug output

```PowerShell
`$secureKey= $storageKey | ConvertTo-SecureString -AsPlainText -Force

$exportRequest = New-AzSqlDatabaseExport -ResourceGroupName $rgName -ServerName $serverName -DatabaseName $dbName -AuthenticationType Sql -StorageKeyType "StorageAccessKey" -StorageKey $secureKey -AdministratorLogin $sqlUser -AdministratorLoginPassword $securePassword -StorageUri $bacpacURL

$importStatus = Get-AzSqlDatabaseImportExportStatus -OperationStatusLink $exportRequest.OperationStatusLink
[Console]::Write("Exporting...")
while ($importStatus.Status -eq "InProgress")
{
$importStatus =Get-AzSqlDatabaseImportExportStatus -OperationStatusLink $exportRequest.OperationStatusLink
[Console]::Write(".")
Start-Sleep -s 10
}
[Console]::WriteLine("")
$importStatus
`
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 7.2.10
PSEdition Core
GitCommitId 7.2.10
OS Microsoft Windows 10.0.20348
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
Name : Az.Accounts
Path : C:\Modules\az_9.3.0\Az.Accounts\2.12.1\Az.Accounts.psm1
Description : Microsoft Azure PowerShell - Accounts credential management cmdlets for Azure Resource Manager in
Windows PowerShell and PowerShell Core.

For more information on account credential management, please visit the following:
https://learn.microsoft.com/powershell/azure/authenticate-azureps
Guid : 17a2feff-488b-47f9-8729-e2cec094624c
Version : 2.12.1
ModuleBase : C:\Modules\az_9.3.0\Az.Accounts\2.12.1
ModuleType : Script
PrivateData : {PSData}
AccessMode : ReadWrite
ExportedAliases : {[Add-AzAccount, Add-AzAccount], [Get-AzDomain, Get-AzDomain], [Invoke-AzRest, Invoke-AzRest],
[Login-AzAccount, Login-AzAccount]…}
ExportedCmdlets : {[Add-AzEnvironment, Add-AzEnvironment], [Clear-AzConfig, Clear-AzConfig], [Clear-AzContext,
Clear-AzContext], [Clear-AzDefault, Clear-AzDefault]…}
ExportedFunctions : {}
ExportedVariables : {}
NestedModules : {Microsoft.Azure.PowerShell.Cmdlets.Accounts}
```

### Error output

_No response_