Update type hints to align util/testing.py and picke.py

Author: TomoyukiSuzuki-Aidea

pandas/util/testing.py

@@ -102,7 +102,7 @@ def reset_display_options():
 
 
 def round_trip_pickle(
-    obj: FrameOrSeries, path: FilePathOrBuffer = None
+    obj: FrameOrSeries, path: Optional[FilePathOrBuffer] = None
 ) -> FrameOrSeries:
     """
     Pickle an object and then read it again.
@@ -111,7 +111,7 @@ def round_trip_pickle(
     ----------
     obj : pandas object
         The object to pickle and then re-read.
-    path : str, default None
+    path : str, path object or file-like object, default None
         The path where the pickled object is written and then read.
 
     Returns