tqdm.dask.TqdmCallback fails without ipywidgets in jupyter notebook

[thomasaarholt]

• I have marked all applicable categories:
  • exception-raising bug
  • visual output bug
• I have visited the source website, and in particular
  read the known issues
• I have searched through the issue tracker for duplicates
• I have mentioned version numbers, operating system and
  environment, where applicable:
  4.62.0 3.9.6 | packaged by conda-forge | (default, Jul 11 2021, 03:35:11)
  [Clang 11.1.0 ] darwin

Without ipywidgets, the dask tqdm callback will raise an error when used in the jupyter notebook:

import dask.array as da
from tqdm.dask import TqdmCallback

with TqdmCallback():
    da.random.random((5,5)).compute()
#raises ImportError: IProgress not found. Please update jupyter and ipywidgets.
# During handling of the above exception, another exception occurred:
...

This is basically the same as #1082.

[thomasaarholt]

Fixed in #1218.