Fix the ros_tutorials branch. (ros2#3631)

For all distributions past Galactic, we have named the
branches after the name of the distribution.  So when
checking out ros_tutorials, we should clone the name of
the distribution, e.g. Humble -> humble, Iron -> iron,
Rolling -> rolling.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

source/Tutorials/Beginner-Client-Libraries/Creating-A-Workspace/Creating-A-Workspace.rst

@@ -130,7 +130,7 @@ In the ``ros2_ws/src`` directory, run the following command:
 
 .. code-block:: console
 
-  git clone https://github.com/ros/ros_tutorials.git -b {DISTRO}-devel
+  git clone https://github.com/ros/ros_tutorials.git -b {DISTRO}
 
 Now ``ros_tutorials`` is cloned in your workspace.  The ``ros_tutorials`` repository contains the ``turtlesim`` package, which we'll use in the rest of this tutorial.  The other packages in this repository are not built because they contain a ``COLCON_IGNORE`` file.