[ci] `unknown parent image ID` in Docker builds

[driazati]

Seen it in many places e.g. https://ci.tlcpack.ai/blue/organizations/jenkins/docker-images-ci%2Fdaily-docker-image-rebuild/detail/daily-docker-image-rebuild/274/pipeline/57

cc @areusch

[driazati]

this should be fixed since we updated the pruning script