[skip ci] Update codes of client file (#11653)

Signed-off-by: wangting0128 <ting.wang@zilliz.com>

tests/benchmark/milvus_benchmark/client.py

@@ -66,6 +66,7 @@ class MilvusClient(object):
     def __init__(self, collection_name=None, host=None, port=None, timeout=300):
         self._collection_name = collection_name
         self._collection_info = None
+        self._dimension = None
         start_time = time.time()
         if not host:
             host = config.SERVER_HOST_DEFAULT