Fix for forward_velocity_controller test (backport #1076)

[mergify]

This PR aims to fix the test for the forward_velocity_controller: basically the related config file was missing the publish_topic parameter. Now when the controller is active, the velocity goals are correctly sent by launching test_forward_velocity_controller.launch.py.

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This is an automatic backport of pull request #1076 done by Mergify.

[mergify]

Cherry-pick of b422d49 has failed:

On branch mergify/bp/humble/pr-1076
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Changes to be committed:
	modified:   ur_robot_driver/config/test_velocity_goal_publishers_config.yaml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   ur_robot_driver/launch/test_forward_velocity_controller.launch.py

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[fmauch]

Seems as if for humble this change is not necessary. The test works without this modification.