The ros2_tracing repository is now on GitHub: GitHub - ros2/ros2_tracing: Tracing tools for ROS 2.
A full summary and the reasoning behind the move can be found here: Moving ros2_tracing to GitHub (#144) · Issues · ros-tracing / ros2_tracing · GitLab. We’ve used this opportunity to also change the default branch name to rolling, as has been done for the other ROS 2 core repositories: Change default branch name to 'rolling' in ROS 2 core.
The now-default rolling branch is being mirrored to the master branch, and the GitLab repository has been set up to mirror the now-official GitHub repository, meaning that this change shouldn’t disrupt anything. However, if you build ROS 2 from source, you should eventually update your workspace (i.e., simply re-import the ros2.repos file). Some scripts and documentation will also need to be updated eventually; I’m working on updating everything that is public.
Happy tracing!