update curl command to handle redirects (#5690)

When running the curl command as described in the link above, I found the server was responding with HTTP error code 302 (temporarily relocated). This can be addressed by allowing curl to follow the relocation by adding -L

crosslink reference: https://discourse.ros.org/t/ros-signing-key-migration-guide/43937/19?u=jbcpollak

Signed-off-by: Joshua Chaitin-Pollak <josh@c11k.org>

Author: jbcpollak

source/Installation/_Apt-Repositories.rst

@@ -16,5 +16,5 @@ Updates to repository configuration will occur automatically when new versions o
 
    $ sudo apt update && sudo apt install curl -y
    $ export ROS_APT_SOURCE_VERSION=$(curl -s https://api.github.com/repos/ros-infrastructure/ros-apt-source/releases/latest | grep -F "tag_name" | awk -F\" '{print $4}')
-   $ curl -o /tmp/ros2-apt-source.deb "https://github.com/ros-infrastructure/ros-apt-source/releases/download/${ROS_APT_SOURCE_VERSION}/ros2-apt-source_${ROS_APT_SOURCE_VERSION}.$(. /etc/os-release && echo $VERSION_CODENAME)_all.deb" # If using Ubuntu derivates use $UBUNTU_CODENAME
+   $ curl -L -o /tmp/ros2-apt-source.deb "https://github.com/ros-infrastructure/ros-apt-source/releases/download/${ROS_APT_SOURCE_VERSION}/ros2-apt-source_${ROS_APT_SOURCE_VERSION}.$(. /etc/os-release && echo $VERSION_CODENAME)_all.deb" # If using Ubuntu derivates use $UBUNTU_CODENAME
    $ sudo apt install /tmp/ros2-apt-source.deb