Add test for trc if i-gain is zero (backport #526)

[mergify]

Follow-up to #511 (comment)

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This is an automatic backport of pull request #526 done by Mergify.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.62%. Comparing base (696a393) to head (0b984d0).

Additional details and impacted files

@@           Coverage Diff           @@
##           kilted     #529   +/-   ##
=======================================
  Coverage   82.61%   82.62%           
=======================================
  Files          29       29           
  Lines        1985     1986    +1     
  Branches      113      113           
=======================================
+ Hits         1640     1641    +1     
  Misses        276      276           
  Partials       69       69           

Flag	Coverage Δ
unittests	82.62% <100.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
control_toolbox/test/pid_tests.cpp	100.00% <100.00%> (ø)

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