Add support for Sensor state class (#1835)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/sgp40/sensor.py

@@ -1,7 +1,13 @@
 import esphome.codegen as cg
 import esphome.config_validation as cv
 from esphome.components import i2c, sensor
-from esphome.const import CONF_ID, DEVICE_CLASS_EMPTY, ICON_RADIATOR, UNIT_EMPTY
+from esphome.const import (
+    CONF_ID,
+    DEVICE_CLASS_EMPTY,
+    ICON_RADIATOR,
+    STATE_CLASS_MEASUREMENT,
+    UNIT_EMPTY,
+)
 
 DEPENDENCIES = ["i2c"]
 
@@ -19,7 +25,9 @@ CONF_STORE_BASELINE = "store_baseline"
 CONF_VOC_BASELINE = "voc_baseline"
 
 CONFIG_SCHEMA = (
-    sensor.sensor_schema(UNIT_EMPTY, ICON_RADIATOR, 0, DEVICE_CLASS_EMPTY)
+    sensor.sensor_schema(
+        UNIT_EMPTY, ICON_RADIATOR, 0, DEVICE_CLASS_EMPTY, STATE_CLASS_MEASUREMENT
+    )
     .extend(
         {
             cv.GenerateID(): cv.declare_id(SGP40Component),