Change tags(str) to tags(dict) in mlflow_callback.py docs (#6473)

Fixes #6472

#### Who can review?

@agola11

langchain/callbacks/mlflow_callback.py

@@ -118,7 +118,7 @@ class MlflowLogger:
     Parameters:
         name (str): Name of the run.
         experiment (str): Name of the experiment.
-        tags (str): Tags to be attached for the run.
+        tags (dict): Tags to be attached for the run.
         tracking_uri (str): MLflow tracking server uri.
 
     This handler implements the helper functions to initialize,
@@ -223,7 +223,7 @@ class MlflowCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
     Parameters:
         name (str): Name of the run.
         experiment (str): Name of the experiment.
-        tags (str): Tags to be attached for the run.
+        tags (dict): Tags to be attached for the run.
         tracking_uri (str): MLflow tracking server uri.
 
     This handler will utilize the associated callback method called and formats