Venstar: define success for all branches of set_temperature() (#26148)

* define success for all branches

* add operation_mode to error when unexpected value

* fix black linting

* black linting

* fix weird black linting result

homeassistant/components/venstar/climate.py

@@ -265,9 +265,11 @@ class VenstarThermostat(ClimateDevice):
             elif operation_mode == self._client.MODE_AUTO:
                 success = self._client.set_setpoints(temp_low, temp_high)
             else:
+                success = False
                 _LOGGER.error(
                     "The thermostat is currently not in a mode "
-                    "that supports target temperature"
+                    "that supports target temperature: %s",
+                    operation_mode,
                 )
 
             if not success: