The boto3 package is used for AWS API. It is used in the https://gitlab.isc.org/isc-projects/bind9-shotgun-ci repository. Pre-installing this package speeds up the tests in that repo.
I've also tried to rebuild the image to check if any update breaks something in bind9 CI. I'm not sure if now is a good time to be updating this image, but as of 2022-06-24, it seems like the update is okay. I only stumbled upon new TSAN failures on v9_18 which may or may not be related to the clang update from 14.0.5 to 14.0.6. There's also an unrelated failure on debian strech due to old Python.