fix: handle poor type inference in count_eigval_multiplicity function

[baggepinnen]

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[JuliaControlBot]

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Plots were compared to references. 3/11 images have changed, see differences below.
After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.52%. Comparing base (3a4e7b6) to head (3c5a5d2).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1001   +/-   ##
=======================================
  Coverage   92.52%   92.52%           
=======================================
  Files          41       41           
  Lines        5095     5095           
=======================================
  Hits         4714     4714           
  Misses        381      381           

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