Fix multi-line strings in DeclareLaunchArgument (backport #948)

[mergify]

Related to:
UniversalRobots/Universal_Robots_ROS2_Description#140
UniversalRobots/Universal_Robots_ROS2_Gazebo_Simulation#59
UniversalRobots/Universal_Robots_ROS2_GZ_Simulation#16

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This is an automatic backport of pull request #948 done by Mergify.

[mergify]

Cherry-pick of d16eaba has failed:

On branch mergify/bp/humble/pr-948
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit d16eaba.
  (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_moveit_config/launch/ur_moveit.launch.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   ur_robot_driver/launch/ur10.launch.py
	both modified:   ur_robot_driver/launch/ur10e.launch.py
	both modified:   ur_robot_driver/launch/ur16e.launch.py
	both modified:   ur_robot_driver/launch/ur20.launch.py
	both modified:   ur_robot_driver/launch/ur3.launch.py
	both modified:   ur_robot_driver/launch/ur30.launch.py
	both modified:   ur_robot_driver/launch/ur3e.launch.py
	both modified:   ur_robot_driver/launch/ur5.launch.py
	both modified:   ur_robot_driver/launch/ur5e.launch.py
	both modified:   ur_robot_driver/launch/ur_control.launch.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