Update lie_closure.py

[CatalinaAlbornoz]

Added clarification about imaginary coefficients in lie_closure.
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[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

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[dwierichs]

Thanks @CatalinaAlbornoz ! 👍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.59%. Comparing base (76b585d) to head (d67ce50).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6983   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files         483      483           
  Lines       46066    46066           
=======================================
  Hits        45881    45881           
  Misses        185      185           

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