Add whatsnew entry

Author: gaogaotiantian

Doc/whatsnew/3.14.rst

@@ -785,6 +785,10 @@ pdb
   (if any).
   (Contributed by Tian Gao in :gh:`130493`.)
 
+* ``<tab>`` at the beginning of the line in :mod:`pdb` multi-line input will
+  fill in a 4-space indentation now, instead of inserting a ``\t`` character.
+  (Contributed by Tian Gao in :gh:`130471`.)
+
 
 pickle
 ------