Description of problem:
Having embedded ipython debugger crashes with ipython 8.4.0, while the same code works fine with 8.5.0.

Version-Release number of selected component (if applicable):
python3-ipython-8.4.0-5.fc37.noarch

How reproducible:
Always

Steps to Reproduce:

from IPython import embed
from traitlets.config import get_config
IPY_DEBUG = True

c = get_config()
c.InteractiveShellEmbed.colors = "Linux"
c.InteractiveShell.pdb = True
embed(config=c)

Actual results:

Traceback (most recent call last):
  File "/home/fanys/devel/oraculum/run_cli.py", line 26, in <module>
    exit = cli.main()
           ^^^^^^^^^^
  File "/home/fanys/devel/oraculum/oraculum/cli.py", line 116, in main
    globals()[args.command]()
  File "/home/fanys/devel/oraculum/oraculum/cli.py", line 105, in debug
    embed(config=c)
  File "/usr/lib/python3.11/site-packages/IPython/terminal/embed.py", line 397, in embed
    shell = InteractiveShellEmbed.instance(_init_location_id='%s:%s' % (
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/traitlets/config/configurable.py", line 551, in instance
    inst = cls(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/IPython/terminal/embed.py", line 172, in __init__
    sys.excepthook = ultratb.FormattedTB(color_scheme=self.colors,
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/IPython/core/ultratb.py", line 994, in __init__
    VerboseTB.__init__(self, color_scheme=color_scheme, call_pdb=call_pdb,
  File "/usr/lib/python3.11/site-packages/IPython/core/ultratb.py", line 638, in __init__
    TBTools.__init__(
  File "/usr/lib/python3.11/site-packages/IPython/core/ultratb.py", line 242, in __init__
    self.pdb = debugger_cls()
               ^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not callable


Expected results:

Working interactive debugger.

Additional info:

8.5.0 (both from fedora rawhide and pip) is verified to be working fine.