Add return type to tests without arguments (#87613)

* Add return type to tests without arguments

* Black

* Cancel fixture amends

tests/components/conversation/test_util.py

@@ -2,7 +2,7 @@
 from homeassistant.components.conversation.util import create_matcher
 
 
-def test_create_matcher():
+def test_create_matcher() -> None:
     """Test the create matcher method."""
     # Basic sentence
     pattern = create_matcher("Hello world")