Subuser throws AttributeError

[Peter]

When invoking subuser, it immediately throws an error. The package doesn't seem to work at all.

```
$ subuser version
Traceback (most recent call last):
  File "/usr/bin/subuser", line 24, in <module>
    command = subuserlib.commands.getCommand(sys.argv[1])
  File "/usr/lib/python3/dist-packages/subuserlib/commands.py", line 49, in getCommand
    commandModule = __import__("subuserlib.builtInCommands."+command, fromlist=[''])
  File "/usr/lib/python3/dist-packages/subuserlib/builtInCommands/version.py", line 11, in <module>
    from subuserlib.classes.user import User
  File "/usr/lib/python3/dist-packages/subuserlib/classes/user.py", line 14, in <module>
    from subuserlib.classes import registry
  File "/usr/lib/python3/dist-packages/subuserlib/classes/registry.py", line 14, in <module>
    from subuserlib.classes import repositories
  File "/usr/lib/python3/dist-packages/subuserlib/classes/repositories.py", line 19, in <module>
    class Repositories(collections.Mapping,UserOwnedObject,FileBackedObject):
AttributeError: module 'collections' has no attribute 'Mapping'
```

Installed package version: subuser 0.6.2-3
Ubuntu version: 22.10