Fix the teardown of the diff_drive_controller test (backport #2183)

[mergify]

Should probably fix ros-controls/ros2_control_ci#665

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This is an automatic backport of pull request #2183 done by Mergify.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.15%. Comparing base (5fdd616) to head (ea7e679).
⚠️ Report is 1 commits behind head on kilted.

Additional details and impacted files

@@           Coverage Diff           @@
##           kilted    #2186   +/-   ##
=======================================
  Coverage   85.15%   85.15%           
=======================================
  Files         151      151           
  Lines       14569    14573    +4     
  Branches     1260     1260           
=======================================
+ Hits        12406    12410    +4     
  Misses       1716     1716           
  Partials      447      447           

Flag	Coverage Δ
unittests	85.15% <100.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
...ive_controller/test/test_diff_drive_controller.cpp	94.21% <100.00%> (+0.03%)	⬆️
...ntroller/test/test_omni_wheel_drive_controller.hpp	86.27% <100.00%> (+0.27%)	⬆️

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