Add state_class to tomorrowio UV Index (home-assistant#98541)

* Added state_class to UV Index

Forgot to add a state_class as other sensors got their state_class from their device class. As there is no UV Index device class I left it out.

* Forgotten a comma, whoops

* Changed measurement to string.

* Changed from "measurement" to SensorStateClass

homeassistant/components/tomorrowio/sensor.py

@@ -18,6 +18,7 @@
     SensorDeviceClass,
     SensorEntity,
     SensorEntityDescription,
+    SensorStateClass,
 )
 from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import (
@@ -295,6 +296,7 @@ def convert_ppb_to_ugm3(molecular_weight: int | float) -> Callable[[float], floa
     TomorrowioSensorEntityDescription(
         key=TMRW_ATTR_UV_INDEX,
         name="UV Index",
+        state_class=SensorStateClass.MEASUREMENT,
         icon="mdi:sun-wireless",
     ),
     TomorrowioSensorEntityDescription(