Corrected variable typo

Update-AzVM takes a <PSVirtualMachine> rather than a <String>.  The previously unused variable $vm was intended to be used with Update-AzVM.  This resolves https://github.com/MicrosoftDocs/azure-docs/issues/89576.

Author: kobulloc-MSFT

articles/virtual-machines/vm-applications-how-to.md

@@ -177,7 +177,7 @@ $appversion = Get-AzGalleryApplicationVersion `
 $packageid = $appversion.Id
 $app = New-AzVmGalleryApplication -PackageReferenceId $packageid
 Add-AzVmGalleryApplication -VM $vmname -GalleryApplication $app
-Update-AzVM -ResourceGroupName $rgname -VM $vmname
+Update-AzVM -ResourceGroupName $rgname -VM $vm
 ```
 
 Verify the application succeeded: