Actually, I figured out what is happening. That step is not hung. The build has moved on to some tar file operation that runs until it fills up the disk and then errors out:

Step 7/12 : RUN groupadd -f -g ${KEDRO_GID} kedro_group && useradd -d /home/kedro -s /bin/bash -g ${KEDRO_GID} -u ${KEDRO_UID} kedro
 ---> Running in eacc1a27e787
Error processing tar file(exit status 1): write /var/log/lastlog: no space left on device

It's filling up over 300 GB of disk so something is not working right. Filing an issue on Github.