The examples were using the default branch of the buildfarm config repo. This branch does no longer work since it references a test farm which is not available anymore. I just updated the examples to point to the production branch instead which is used by the official buildfarm and will continue to be available: https://github.com/ros-infrastructure/ros_buildfarm/pull/390
The README in https://github.com/ros-infrastructure/ros_buildfarm_config mentions the different branches but the information is bit “hidden” in the text and not easy to discover.