Fix: AttributeError: 'MicroVM' object has no attribute 'send_shutdown…

…_message'

Error reported on #652

src/aleph/vm/controllers/__main__.py

@@ -86,6 +86,7 @@ async def handle_persistent_vm(config: Configuration, execution: Union[MicroVM,
     def callback():
         """Callback for the signal handler to stop the VM and cleanup properly on SIGTERM."""
         loop.create_task(execution.teardown())
+
     loop.add_signal_handler(signal.SIGTERM, callback)
 
     await process.wait()