tests (device): use non-async mock for receive_loop

tests/test_device.py

@@ -373,7 +373,7 @@ class TestDevice(IsolatedAsyncioTestCase):
 
     def test_actually_start(self):
         # Set up the preconditions
-        self.subject.receive_loop = AsyncMock()
+        self.subject.receive_loop = Mock()
         self.subject.receive_loop.return_value = "LOOP"
         self.hass().bus.async_listen_once.return_value = "LISTENER"
         self.hass().async_create_task = Mock()