skip Lorentz2D until it can be supported

[braingram]

astropy added astropy.modeling.functional_models.Lorentz2D see #243

This PR adds the unsupported model to the list of unsupported models to fix the devdeps.

This PR does not close the associated issue as we'll need to:

• make a schema
• add the schema to asdf-transform-schemas
• add a converter to this package

so let's leave the issue open to track that work.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.44%. Comparing base (51ede39) to head (c2aced3).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...tropy/converters/transform/tests/test_transform.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #244   +/-   ##
=======================================
  Coverage   99.44%   99.44%           
=======================================
  Files          54       54           
  Lines        1992     1994    +2     
=======================================
+ Hits         1981     1983    +2     
  Misses         11       11           

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