Update humble repos file (#750)

Author: christophfroehlich

ros2_control_demos.humble.repos

@@ -15,9 +15,9 @@ repositories:
     type: git
     url: https://github.com/ros-controls/ros2_controllers.git
     version: humble
-  gazebo_ros2_control:
+  gz_ros2_control:
     type: git
-    url: https://github.com/ros-controls/gazebo_ros2_control.git
+    url: https://github.com/ros-controls/gz_ros2_control.git
     version: humble
   control_toolbox:
     type: git