[Merge] ~andersson123/ubuntu-release-upgrader:fix_distupgradequirks_traceback into ubuntu-release-upgrader:ubuntu/main

[Paride Legovini]

Ideally we should have a bug describing what we are fixing here, especially given that this is a last minute fix, it's nice to have a pointer to why it was uploaded. Also we can reference the bug in the release tracking document.

If you file a bug, mention it somewhere in the commit message as e.g. `LP: #12345`, and let `gbo-dch` auto-reference it in the generated d/changelog entry.
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https://code.launchpad.net/~andersson123/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/453214
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