Add history_graph component to demo (#12681)

tests/components/test_demo.py

@@ -10,6 +10,12 @@ from homeassistant.components import demo, device_tracker
 from homeassistant.remote import JSONEncoder
 
 
+@pytest.fixture(autouse=True)
+def mock_history(hass):
+    """Mock history component loaded."""
+    hass.config.components.add('history')
+
+
 @pytest.fixture
 def minimize_demo_platforms(hass):
     """Cleanup demo component for tests."""