Changed msg's explanation

Author: Manoj

Doc/library/asyncio-future.rst

@@ -198,7 +198,7 @@ Future Object
 
       The optional argument *msg* is passed as the argument to the
       :exc:`CancelledError` exception raised when a cancelled Future
-      is awaited. It can be any object.
+      is awaited. It is typically a string.
 
       .. versionchanged:: 3.9
          Added the *msg* parameter.