[BUG] GroundTruthAgreement is not working with Litellm

[Arslan-Soomro]

Bug Description
I am using ground truth agreement feedback function, and the when I print the result for that feedback, it is none. all other feedbacks work okay though.

To Reproduce

    from trulens.providers.litellm import LiteLLM
    from trulens.core import TruSession, Feedback
    from trulens.feedback import GroundTruthAgreement
    from trulens.apps.llamaindex import TruLlama

    trulens_provider = Litellm(model)
    qa_dataset = [{"query": "Who are you?", "response": "I am an ai Chatbot"}]
    f_groundtruth = Feedback(
        GroundTruthAgreement(
            ground_truth=qa_dataset, 
            provider=trulens_provider
        ).agreement_measure, name="Answer Correctness"
    ).on_input_output()
   
    tru_recorder = TruLlama(
        query_engine,
        app_name="Naive RAG Eval Llama",
        app_version="1.0",
        feedbacks=[f_groundtruth],
    )

    with tru_recorder as recording:
            query_engine.query(qa_dataset[0]["query"]);
    
    rec = recording.get();
    for feedback, feedback_result in rec.wait_for_feedback_results().items():
            print(f"{feedback.name}: {feedback_result.result}")

Expected behavior
groundtruth feedback should provide the score for answer correctness in the result.

Environment:

• OS: MacOS
• Python Version: 3.12
• TruLens version: 1.2.7