Add test_depend on hardware_interface_testing also for diff_drive

[christophfroehlich]

I forgot diff_drive_controller with #1018
https://github.com/ros-controls/ros2_controllers/actions/runs/7781428588/job/21215842755

[codecov]

Codecov Report

Attention: 37 lines in your changes are missing coverage. Please review.

Comparison is base (9f7e9e9) 47.71% compared to head (b545ac7) 47.82%.
Report is 15 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1021      +/-   ##
==========================================
+ Coverage   47.71%   47.82%   +0.11%     
==========================================
  Files          41       41              
  Lines        3871     3818      -53     
  Branches     1833     1783      -50     
==========================================
- Hits         1847     1826      -21     
- Misses        751      771      +20     
+ Partials     1273     1221      -52     

Flag	Coverage Δ
unittests	47.82% <31.48%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...de/diff_drive_controller/diff_drive_controller.hpp	100.00% <ø> (ø)
...iff_drive_controller/src/diff_drive_controller.cpp	42.85% <100.00%> (-5.20%)	⬇️
...nclude/tricycle_controller/tricycle_controller.hpp	100.00% <ø> (ø)
...roadcaster/src/force_torque_sensor_broadcaster.cpp	59.70% <50.00%> (-0.91%)	⬇️
...ory_controller/src/joint_trajectory_controller.cpp	46.87% <25.00%> (-0.25%)	⬇️
tricycle_controller/src/tricycle_controller.cpp	38.38% <21.21%> (+5.72%)	⬆️

... and 1 file with indirect coverage changes