don't load CS for tests of CSBase

[baggepinnen]

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[JuliaControlBot]

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

Difference	Reference Image	New Image
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❌ 0.034
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[codecov]

Codecov Report

Merging #756 (782c84a) into master (b401918) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #756      +/-   ##
==========================================
+ Coverage   94.48%   94.50%   +0.01%     
==========================================
  Files           3        4       +1     
  Lines         290      291       +1     
==========================================
+ Hits          274      275       +1     
  Misses         16       16              

Impacted Files	Coverage Δ
src/ControlSystems.jl	100.00% <0.00%> (ø)

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