The commands were grouped like that because they are part of a RUN in a Dockerfile. The build was happening on a Github Actions runner, so not so easy to just interactively run them one at a time. But, I'm pretty confident that it was the "debuild -b -uc -us" that failed.
I have since gathered some more information. I started an Ubuntu-22.04 EC2 arm instance (because I don't have access to an arm machine any other way) and ran the commands and they all completed and built the RPMs just fine. My container, however, is using Ubuntu-20.04. Unfortunately, the arm architecture is not available for the Ubuntu 20.04 AMI on EC2 (at least for me), so I was not able to do a clean test of 20.04. I suspect it's a problem with 20.04, and that 22.04+ is required. I can add a "mxschmitt/action-tmate@v3" github action to my CI step to try to get an interactive access to the github runner at failure time and see if I can reproduce the failure manually. I was hoping not to update to 20.04 yet due to downstream dependencies for my container, but it looks like that might be unavoidable.