Add and use percentage constant (#32094)

* Add and use percentage constant

* Fix pylint error and broken test

homeassistant/components/bme280/sensor.py

@@ -8,7 +8,12 @@ import smbus  # pylint: disable=import-error
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_MONITORED_CONDITIONS, CONF_NAME, TEMP_FAHRENHEIT
+from homeassistant.const import (
+    CONF_MONITORED_CONDITIONS,
+    CONF_NAME,
+    TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import Throttle
@@ -44,7 +49,7 @@ SENSOR_HUMID = "humidity"
 SENSOR_PRESS = "pressure"
 SENSOR_TYPES = {
     SENSOR_TEMP: ["Temperature", None],
-    SENSOR_HUMID: ["Humidity", "%"],
+    SENSOR_HUMID: ["Humidity", UNIT_PERCENTAGE],
     SENSOR_PRESS: ["Pressure", "mb"],
 }
 DEFAULT_MONITORED = [SENSOR_TEMP, SENSOR_HUMID, SENSOR_PRESS]