Add return type to async tests without arguments (#87612)

tests/components/binary_sensor/test_significant_change.py

@@ -4,7 +4,7 @@ from homeassistant.components.binary_sensor.significant_change import (
 )
 
 
-async def test_significant_change():
+async def test_significant_change() -> None:
     """Detect Binary Sensor significant changes."""
     old_attrs = {"attr_1": "value_1"}
     new_attrs = {"attr_1": "value_2"}