use DifferentiationInterface in the landau model

[KristofferC]

Ref https://github.com/Ferrite-FEM/Ferrite.jl/issues/1229

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 0.00%. Comparing base (7a428b0) to head (7b9dd9d).

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1258   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files          40      40           
  Lines        6572    6572           
======================================
  Misses       6572    6572           

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