test: Add client fixture override for runnable vertices manager unit test. (#3430)

src/backend/tests/unit/graph/graph/test_runnable_vertices_manager.py

@@ -6,6 +6,11 @@ import pytest
 from langflow.graph.graph.runnable_vertices_manager import RunnableVerticesManager
 
 
+@pytest.fixture
+def client():
+    pass
+
+
 @pytest.fixture
 def data():
     run_map: defaultdict(list) = {"A": ["B", "C"], "B": ["D"], "C": ["D"], "D": []}