fix flake8 build error due to missing stacklevel argument for warn method

[imatiach-msft]

Seeing gated builds fail due to new errors:

./python/interpret_community/mimic/models/linear_model.py:45:[13](https://github.com/interpretml/interpret-community/actions/runs/4264305493/jobs/7422204144#step:6:14): B028 No explicit stacklevel keyword argument found. The warn method from the warnings module uses a stacklevel of 1 by default. This will only show a stack trace for the line on which the warn method is called. It is therefore recommended to use a stacklevel of 2 or greater to provide more information to the user.
./python/interpret_community/widget/explanation_dashboard.py:55:9: B028 No explicit stacklevel keyword argument found. The warn method from the warnings module uses a stacklevel of 1 by default. This will only show a stack trace for the line on which the warn method is called. It is therefore recommended to use a stacklevel of 2 or greater to provide more information to the user.
./tests/common_utils.py:160:9: B028 No explicit stacklevel keyword argument found. The warn method from the warnings module uses a stacklevel of 1 by default. This will only show a stack trace for the line on which the warn method is called. It is therefore recommended to use a stacklevel of 2 or greater to provide more information to the user.

These warnings seem to have been added to the newer releases of flake8-bugbear extension package to flake8.

This PR fixes the error by explicitly setting the stacklevel argument on the warn method call. It seems it is recommended to set it to level 2 as it creates better warning messages by excluding the warn method itself from the printed stacktrace which can be confusing.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.83%. Comparing base (788c9e4) to head (4d52fb4).
⚠️ Report is 41 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #554   +/-   ##
=======================================
  Coverage   87.83%   87.83%           
=======================================
  Files          62       62           
  Lines        4094     4094           
=======================================
  Hits         3596     3596           
  Misses        498      498           

Flag	Coverage Δ
unittests	87.83% <ø> (ø)

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