Fix Update-AzFunctionApp -InputObject $functionApp to work on Playback mode

### Description

Currently, the `Update-AzFunctionApp -InputObject $functionApp` tests are failing on Playback because the parameters (`$HttpPipelineAppend` and `$HttpPipelinePrepend`) used for playback are not properly populated.

Scenario:
Update-AzFunctionApp -InputObject $functionApp

In the cmdlet logic, we make a call to retrieve the app settings (previously the app settings were appended to the $functionApp object).

Need to follow up with the Azure-PowerShell team on how to fix this.

### Issue script & Debug output

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### Environment data

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### Module versions

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### Error output

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