python310Packages.ipdb: propagate exceptiongroup for older python

This is a builtin only available from python 3.11.

pkgs/development/python-modules/ipdb/default.nix

···
 , decorator
 , ipython
 , isPyPy
+, exceptiongroup
 , tomli
 , setuptools
 , unittestCheckHook
···
     ipython
     decorator
   ] ++ lib.optionals (pythonOlder "3.11") [
+    exceptiongroup
     tomli
   ];