Fix passing launch_dashobard_client launch argument (backport #1057)

[mergify]

This was not handled properly.

This fixes #1056

ToDo:

• Add test

  ---

  This is an automatic backport of pull request Fix passing launch_dashobard_client launch argument #1057 done by Mergify.

[mergify]

Cherry-pick of ca19535 has failed:

On branch mergify/bp/humble/pr-1057
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit ca19535.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   ur_robot_driver/CMakeLists.txt
	new file:   ur_robot_driver/test/launch_args.py

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

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[fmauch]

Conflicts are resolved, ready to ship it unless the CI opposes.