Use warning attribute of RcutilsLogger

[saikishor]

Might lead to similar errors like ros-controls/ros2_control#2243

It looks like the warn method is deprecated long back and they have removed it recently in ros2/rclpy#1456

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 85.69%. Comparing base (dc53641) to head (a6f155d).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...est_nodes/publisher_joint_trajectory_controller.py	0.00%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1690   +/-   ##
=======================================
  Coverage   85.69%   85.69%           
=======================================
  Files         123      123           
  Lines       11896    11896           
  Branches     1015     1015           
=======================================
  Hits        10194    10194           
  Misses       1379     1379           
  Partials      323      323           

Flag	Coverage Δ
unittests	85.69% <0.00%> (ø)

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

Files with missing lines	Coverage Δ
...est_nodes/publisher_joint_trajectory_controller.py	59.09% <0.00%> (ø)

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[christophfroehlich]

Thank you!