Code review comment for ~jawn-smith/ubuntu/+source/ubuntu-release-upgrader:ubuntu/jammy

If you are going to add python3-yaml as a dependency in jammy, then it should either (1) be SRU'd to focal and impish, or (2) there should be logic to handle a potential import exception.

This recently came up in bug 1965568, i.e. I learned this the hard way.