Ignore error code from `apt-get purge` (#40631)
Summary:
This replicates the pattern of other "do for luck" commands.
Prep change to add RocM to CircleCI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40631
Differential Revision: D22261707
Pulled By: malfet
fbshipit-source-id: 3dadfa434deab866a8800715f3197e84169cf43e
