fix: Fix milvus online_read

[ntkathole]

What this PR does / why we need it:

Fixes get_online_features for milvus:

"/Users/farceo/dev/feast/sdk/python/feast/infra/online_stores/online_store.py", line 199, in get_online_features
    read_rows = self.online_read(
  File "/Users/farceo/dev/feast/sdk/python/feast/infra/online_stores/milvus_online_store/milvus.py", line 421, in online_read
    type(getattr(val, proto_attr)).__args__[0],
AttributeError: __args__

After fix:

def run_entity_retrieval_demo():
    entity_retrieved_features = store.get_online_features(
        features=[
            "docling_transform_docs:vector",
            "docling_transform_docs:chunk_id",
            "docling_transform_docs:chunk_text",
            "docling_transform_docs:document_id",
        ],
        entity_rows=[{"document_id": "doc-1", "chunk_id": "chunk-1"}],
    )
    print("docling transformed features retrieved via entity =")
    print(entity_retrieved_features.to_df())

Connecting to Milvus in local mode using data/online_store.db
docling transformed features retrieved via entity =
  document_id chunk_id                                         chunk_text                                             vector
0       doc-1  chunk-1  a. Picture of a table:\nTables organize valuab...  [0.05077127367258072, -0.005573314614593983, -...

[franciscojavierarceo]

@ntkathole looks like tests are failing. DQM has been failing for a bit so surprised I'm seeing it here now.