UnboundLocalError: local variable 'success' referenced before assignment

https://sentry.softwareheritage.org/organizations/swh/issues/9871/?referrer=phabricator_plugin

SystemExit: -241
(2 additional frame(s) were not displayed)
...
  File "swh/loader/git/loader.py", line 431, in get_directories
    yield converters.dulwich_tree_to_directory(raw_obj)
  File "swh/loader/git/converters.py", line 124, in dulwich_tree_to_directory
    target=hash_to_bytes(entry.sha.decode("ascii")),
  File "<attrs generated init swh.model.model.DirectoryEntry>", line 10, in __init__
  File "billiard/common.py", line 119, in _shutdown_cleanup
    sys.exit(-(256 - signum))
  File "billiard/pool.py", line 283, in exit
    return _exit(status)

UnboundLocalError: local variable 'success' referenced before assignment
  File "swh/scheduler/task.py", line 61, in __call__
    result = super().__call__(*args, **kwargs)
  File "celery/app/trace.py", line 734, in __protected_call__
    return self.run(*args, **kwargs)
  File "swh/loader/git/tasks.py", line 25, in load_git
    return loader.load()
  File "swh/loader/core/loader.py", line 435, in load
    "flush", tags={"success": success, "status": status}

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Migrated from T4236 (view on Phabricator)