Move icon constants to entity attributes (#90518)

* Move icon constants to attribute

* Adjust test

homeassistant/components/smappee/switch.py

@@ -10,7 +10,6 @@ from homeassistant.helpers.entity_platform import AddEntitiesCallback
 from .const import DOMAIN
 
 SWITCH_PREFIX = "Switch"
-ICON = "mdi:toggle-switch"
 
 
 async def async_setup_entry(
@@ -55,6 +54,8 @@ async def async_setup_entry(
 class SmappeeActuator(SwitchEntity):
     """Representation of a Smappee Comport Plug."""
 
+    _attr_icon = "mdi:toggle-switch"
+
     def __init__(
         self,
         smappee_base,
@@ -105,11 +106,6 @@ class SmappeeActuator(SwitchEntity):
         # Switch or comfort plug
         return self._state == "ON_ON"
 
-    @property
-    def icon(self):
-        """Icon to use in the frontend."""
-        return ICON
-
     def turn_on(self, **kwargs: Any) -> None:
         """Turn on Comport Plug."""
         if self._actuator_type in ("SWITCH", "COMFORT_PLUG"):