Use TestCase.addCleanup (#36560)

tests/components/panel_iframe/test_init.py

@@ -14,10 +14,7 @@ class TestPanelIframe(unittest.TestCase):
     def setUp(self):
         """Set up things to be run when tests are started."""
         self.hass = get_test_home_assistant()
-
-    def tearDown(self):
-        """Stop everything that was started."""
-        self.hass.stop()
+        self.addCleanup(self.hass.stop)
 
     def test_wrong_config(self):
         """Test setup with wrong configuration."""