context.py: illegal import of deb822

[xypron]

Pylint shows these coding errors:

  livefs_edit/context.py:235:8:
    E0401: Unable to import 'deb822' (import-error)
    C0415: Import outside toplevel (deb822.Deb822)
           (import-outside-toplevel)

'deb822' can be imported from 'debian'.

Fixes: 4d5ff31 ("rewrite get_suite in an excessively fancy way")

[mwhudson]

The reason for doing it this way was to avoid python3-debian being a requirement for uses that did not need it. I don't know how relevant that is really -- but maybe you could add a try: / except ImportError: around the top level import?

[xypron]

The dependency is clearly stated in README.md.
The package python3-debian is available in Focal and all later releases.
Adding a try block would not stop the code from failing when entering get-suite.