Add typing to smartthings climate target_temperature_low (#143713)

Fix climate target_temperature_low

homeassistant/components/smartthings/climate.py

@@ -307,7 +307,7 @@ class SmartThingsThermostat(SmartThingsEntity, ClimateEntity):
         return None
 
     @property
-    def target_temperature_low(self):
+    def target_temperature_low(self) -> float | None:
         """Return the lowbound target temperature we try to reach."""
         if self.hvac_mode == HVACMode.HEAT_COOL:
             return self.get_attribute_value(