ur_moveit_config: Assure the description is loaded as string (#1452)

Otherwise the description might get loaded as yaml under certain situations.

Author: urfeex

ur_moveit_config/launch/ur_moveit.launch.py

@@ -34,6 +34,7 @@
 from launch_ros.actions import Node
 from launch_ros.substitutions import FindPackageShare
 from ur_moveit_config.launch_common import load_yaml
+from launch_ros.parameter_descriptions import ParameterValue
 
 from launch import LaunchDescription
 from launch.actions import DeclareLaunchArgument, OpaqueFunction
@@ -125,7 +126,9 @@ def launch_setup(context, *args, **kwargs):
             " ",
         ]
     )
-    robot_description = {"robot_description": robot_description_content}
+    robot_description = {
+        "robot_description": ParameterValue(robot_description_content, value_type=str)
+    }
 
     # MoveIt Configuration
     robot_description_semantic_content = Command(