vine: manager shutdown=True parameter raises AttributeError

[EamonTracey]

The ndcctools.taskvine.Manager class has a shutdown parameter. If set to true, the manager should shutdown all workers when the manager finishes. However, an AttributeError is raised.

import ndcctools.taskvine as vine
manager = vine.Manager(shutdown=True)

Exception ignored in: <function Manager.__del__ at 0x7f731bd7c220>
Traceback (most recent call last):
  File "./python3.12/site-packages/ndcctools/taskvine/manager.py", line 160, in __del__
  File "./python3.12/site-packages/ndcctools/taskvine/manager.py", line 152, in _free
AttributeError: 'Manager' object has no attribute 'shutdown_workers'

The issue seems to be that the nonexistent method shutdown_workers is called. Instead, workers_shutdown is the correct method.