Fix mock_sensor_commands variable name for Robotiq macro on Humble

[scastro-bdai]

The ros2_robotiq_gripper repo on Humble uses mock_sensor_commands as its macro name, so this fixes things.

source:

• https://github.com/PickNikRobotics/ros2_robotiq_gripper/blob/e5656b1c1926864899dfb133dc68d483cfb1d9cc/robotiq_description/urdf/robotiq_2f_85_macro.urdf.xacro#L13
• https://github.com/PickNikRobotics/ros2_robotiq_gripper/blob/e5656b1c1926864899dfb133dc68d483cfb1d9cc/robotiq_description/urdf/robotiq_2f_140_macro.urdf.xacro#L13

[aalmrad]

@scastro-bdai, it seems that a lot of nomenclature modifications are being implemented recently, as such I am currently relying on a fork of the ros2_robotiq_gripper repository until things become more stable.