fix: Add async aupdate_build_config to CustomComponent (#5181)

* Add async aupdate_build_config to CustomComponent

* Add test of backward compatibility

src/backend/tests/unit/custom/custom_component/test_component.py

@@ -1,10 +1,15 @@
+from typing import Any
+
 import pytest
 from langflow.components.agents import AgentComponent
 from langflow.components.crewai import CrewAIAgentComponent, SequentialTaskComponent
+from langflow.components.custom_component import CustomComponent
 from langflow.components.inputs import ChatInput
 from langflow.components.models import OpenAIModelComponent
 from langflow.components.outputs import ChatOutput
+from langflow.schema import dotdict
 from langflow.template import Output
+from typing_extensions import override
 
 
 def test_set_invalid_output():
@@ -58,3 +63,21 @@ def test_set_required_inputs_various_components():
     assert _assert_all_outputs_have_different_required_inputs(chatoutput.outputs)
     assert _assert_all_outputs_have_different_required_inputs(task.outputs)
     assert _assert_all_outputs_have_different_required_inputs(agent.outputs)
+
+
+async def test_update_build_config_backward_compatibility():
+    class TestComponent(CustomComponent):
+        @override
+        def update_build_config(
+            self,
+            build_config: dotdict,
+            field_value: Any,
+            field_name: str | None = None,
+        ):
+            build_config["foo"] = "bar"
+            return build_config
+
+    component = TestComponent()
+    build_config = dotdict()
+    build_config = await component.aupdate_build_config(build_config, "", "")
+    assert build_config["foo"] == "bar"