Fix implicit-return in surepetcare tests (#122785)

tests/components/surepetcare/conftest.py

@@ -17,6 +17,7 @@ from tests.common import MockConfigEntry
 async def _mock_call(method, resource):
     if method == "GET" and resource == MESTART_RESOURCE:
         return {"data": MOCK_API_DATA}
+    return None
 
 
 @pytest.fixture