fix: memory leak in UTMAppleVirtualMachine when installation fails

Clear progressObserver and installProgress in the error path of
installVM() to break the retain cycle caused by the KVO observation
closure capturing self strongly.

Services/UTMAppleVirtualMachine.swift

@@ -582,6 +582,8 @@ final class UTMAppleVirtualMachine: UTMVirtualMachine {
             throw UTMAppleVirtualMachineError.operatingSystemInstallNotSupported
             #endif
         } catch {
+            progressObserver = nil
+            installProgress = nil
             await stopAccesingResources()
             delegate?.virtualMachine(self, didCompleteInstallation: false)
             state = .stopped