text: Title: SyntaxWarning: "is" with a literal. Did you mean "=="?
  Body: Hi all!
  
  If I install python>=3.8.1 and segmentation-models-pytorch==0.32.2, then an warning occurs on import `import segmentation_models_pytorch as smp`. The warning appears in library `pretrainedmodels`.
  
  ```
  Python 3.9.15 (main, Mar 13 2023, 09:18:54) 
  [GCC 7.5.0] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import segmentation_models_pytorch as smp
  /home/jovyan/.cache/pypoetry/virtualenvs/s-outer-seg-sem-facade-mvp280223smp-82NsP1dj-py3.9/lib/python3.9/site-packages/pretrainedmodels/models/dpn.py:255: SyntaxWarning: "is" with a literal. Did you mean "=="?
    if block_type is 'proj':
  /home/jovyan/.cache/pypoetry/virtualenvs/s-outer-seg-sem-facade-mvp280223smp-82NsP1dj-py3.9/lib/python3.9/site-packages/pretrainedmodels/models/dpn.py:258: SyntaxWarning: "is" with a literal. Did you mean "=="?
    elif block_type is 'down':
  /home/jovyan/.cache/pypoetry/virtualenvs/s-outer-seg-sem-facade-mvp280223smp-82NsP1dj-py3.9/lib/python3.9/site-packages/pretrainedmodels/models/dpn.py:262: SyntaxWarning: "is" with a literal. Did you mean "=="?
    assert block_type is 'normal'
  ```
  
  The warning disappears when I install python 3.7.5.
  
  In segmentation version 0.3.1 updated `Codebase refactoring and style checks (black, flake8)`. I think the problem is in the flake8. And in python 3.7.5. maybe flake8 is being ignored.
  
  Is there a way to disable flake8? To turn off the warning python >= 3.8.