TypeError with multi backend

[Tommy Nguyen]

This is similar to https://bugs.launchpad.net/duplicity/+bug/1851727

duplicity 0.8.07
Python 3.7.5
Fedora 31
Linux
$ duplicity collection-status
'multi:///home/tom/duplicity.json?mode=mirror'

My duplicity.json contains the following contents:

[
    {
        "description": "second drive",
        "url": "file:///home/tom/second_drive/backup/"
    },
    {
        "description": "third drive",
        "url": "file:///home/tom/third_drive/backup/"
    }
]

The command results in the following stacktrace:

Traceback (innermost last):
  File "/usr/bin/duplicity", line 101, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 87, in with_tempdir
    fn()
  File "/usr/lib64/python3.7/site-packages/duplicity/dup_main.py", line 1539, in main
    do_backup(action)
  File "/usr/lib64/python3.7/site-packages/duplicity/dup_main.py", line 1561, in do_backup
    action).set_values()
  File "/usr/lib64/python3.7/site-packages/duplicity/dup_collections.py", line 745, in set_values
    self.get_backup_chains(partials + backend_filename_list)
  File "/usr/lib64/python3.7/site-packages/duplicity/dup_collections.py", line 897, in get_backup_chains
    add_to_chains(s)
  File "/usr/lib64/python3.7/site-packages/duplicity/dup_collections.py", line 889, in add_to_chains
    if chain.add_inc(set):
  File "/usr/lib64/python3.7/site-packages/duplicity/dup_collections.py", line 358, in add_inc
    incset.end_time > self.incset_list[-1]):
 TypeError: '>' not supported between instances of 'int' and 'BackupSet'

This looks like a typo. Changing line 358 to "incset.end_time > self.incset_list[-1].end_time" appears to fix the error.