Fix input_scitype for AffinityPropagation

[ablaom]

input_scitype works a bit differently for Static models; see https://juliaai.github.io/MLJModelInterface.jl/dev/static_models/#Static-models

This patch fixes the trait for Affinity Propagation.

The problem is causing integration tests to fail at MLJ.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.77%. Comparing base (3d4b729) to head (8a246e2).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #30   +/-   ##
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  Coverage   96.77%   96.77%           
=======================================
  Files           1        1           
  Lines          93       93           
=======================================
  Hits           90       90           
  Misses          3        3           

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