minor grammar mistake (ros2#2698) (ros2#2700)

(cherry picked from commit 128644e)

Co-authored-by: Adum888 <33115304+Adum888@users.noreply.github.com>

source/How-To-Guides/Launch-file-different-formats.rst

@@ -298,6 +298,6 @@ However, if your launch file requires flexibility that you cannot achieve with X
 Using Python for ROS 2 launch is more flexible because of following two reasons:
 
 * Python is a scripting language, and thus you can leverage the language and its libraries in your launch files.
-* `ros2/launch <https://github.com/ros2/launch>`_ (general launch features) and `ros2/launch_ros <https://github.com/ros2/launch_ros>`_ (ROS 2 specific launch features) are written in Python and thus you have lower level access to launch features that may not exposed by XML and YAML.
+* `ros2/launch <https://github.com/ros2/launch>`_ (general launch features) and `ros2/launch_ros <https://github.com/ros2/launch_ros>`_ (ROS 2 specific launch features) are written in Python and thus you have lower level access to launch features that may not be exposed by XML and YAML.
 
 That being said, a launch file written in Python may be more complex and verbose than one in XML or YAML.