Hold a lock to prevent concurrent setup of config entries (#116482)

tests/components/mqtt/test_init.py

@@ -1873,6 +1873,7 @@ async def test_reload_entry_with_restored_subscriptions(
     # Setup the MQTT entry
     entry = MockConfigEntry(domain=mqtt.DOMAIN, data={mqtt.CONF_BROKER: "test-broker"})
     entry.add_to_hass(hass)
+    hass.config.components.add(mqtt.DOMAIN)
     mqtt_client_mock.connect.return_value = 0
     with patch("homeassistant.config.load_yaml_config_file", return_value={}):
         await entry.async_setup(hass)