Issue #25464: Fixed HList.header_exists() in tkinter.tix module by addin

a workaround to Tix library bug.

diff --cc Misc/NEWS
index 2eea9582d6e2288401ff718fd941d571bde023a1,5f005206f7d34a4bd84306257e51daa06af05558..133949e45778cf38b16e548aaa5e7fec833c6fcd
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -16,6 -16,16 +16,9 @@@ Core and Builtin
  - Issue #23782: Fixed possible memory leak in _PyTraceback_Add() and exception
    loss in PyTraceBack_Here().
  
 -- Issue #28471: Fix "Python memory allocator called without holding the GIL"
 -  crash in socket.setblocking.
 -
 -
 -Library
 --------
 -
+ - Issue #25464: Fixed HList.header_exists() in tkinter.tix module by addin
+   a workaround to Tix library bug.
+ 
  - Issue #28488: shutil.make_archive() no longer adds entry "./" to ZIP archive.
  
  - Issue #25953: re.sub() now raises an error for invalid numerical group