Update T1021.003.yaml

Fixing yaml error

atomics/T1021.003/T1021.003.yaml

@@ -23,6 +23,7 @@ atomic_tests:
       [activator]::CreateInstance([type]::GetTypeFromProgID("MMC20.application","#{computer_name}")).Document.ActiveView.ExecuteShellCommand("c:\windows\system32\calc.exe", $null, $null, "7")
     name: powershell
 - name: PowerShell Lateral Movement Using Excel Application Object
+  auto_generated_guid: b46d327c-c336-43d9-906e-d53be5358535
   description: |
     Powershell lateral movement using the Excel COM objects.
 
@@ -47,7 +48,7 @@ atomic_tests:
     cleanup_command: |
       Remove-Item 'C:\users\#{user}\AppData\local\Microsoft\WindowsApps\foxprow.exe'
   input_arguments:
-    computer_name: hostname
+    hostname:
       description: Hostname or IP
       type: string
       default: localhost