traitlets needs to be pinned to 5.9.0

[bakeromso]

I get the error

$ python -m jupyter notebook
Traceback (most recent call last):
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/notebook/traittypes.py", line 235, in _resolve_classes
    klass = self._resolve_string(klass)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/traitlets.py", line 2018, in _resolve_string
    return import_item(string)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/utils/importstring.py", line 31, in import_item
    module = __import__(package, fromlist=[obj])
ModuleNotFoundError: No module named 'jupyter_server.contents'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/user/.pyenv/versions/cw/bin/jupyter-notebook", line 8, in <module>
    sys.exit(main())
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/jupyter_core/application.py", line 281, in launch_instance
    super().launch_instance(argv=argv, **kwargs)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/config/application.py", line 1075, in launch_instance
    app = cls.instance(**kwargs)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/config/configurable.py", line 583, in instance
    inst = cls(*args, **kwargs)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/traitlets.py", line 1294, in __new__
    inst.setup_instance(*args, **kwargs)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/traitlets.py", line 1337, in setup_instance
    super(HasTraits, self).setup_instance(*args, **kwargs)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/traitlets/traitlets.py", line 1313, in setup_instance
    init(self)
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/notebook/traittypes.py", line 226, in instance_init
    self._resolve_classes()
  File "/home/user/.pyenv/versions/cw/lib/python3.9/site-packages/notebook/traittypes.py", line 238, in _resolve_classes
    warn(f"{klass} is not importable. Is it installed?", ImportWarning)
TypeError: warn() missing 1 required keyword-only argument: 'stacklevel'

As suggested by https://stackoverflow.com/questions/77549493/modulenotfounderror-no-module-named-jupyter-server-contents, this is solved by uninstalling traitlets and reinstalling to fixed version of 5.9.0. I suggest to add it to requirements.txt, but I can´t test it right. However, reinstalling and installing to this version fixes this issue for me.

[prockallsyms]

This is no longer the case, instead notebook should be pinned at 6.5.6 due to recent patches.