ManagedGroup.anvil_audit_membership fails when the app service account is not a direct admin of a group

[amstilp]

This bug occurs when:

• The service account is not a direct admin of a group, but is an admin via another group that is an admin of the first group.

Result: The audit succeeds.

Expected result: The audit fails with a 500 server error and the following traceback:

Traceback (most recent call last):
  File "venv/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "venv/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3.8/contextlib.py", line 75, in inner
    return func(*args, **kwds)
  File "venv/lib/python3.8/site-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "venv/lib/python3.8/site-packages/django/contrib/auth/mixins.py", line 104, in dispatch
    return super().dispatch(request, *args, **kwargs)
  File "venv/lib/python3.8/site-packages/django/views/generic/base.py", line 98, in dispatch
    return handler(request, *args, **kwargs)
  File "venv/lib/python3.8/site-packages/anvil_consortium_manager/views.py", line 97, in get
    self.run_audit()
  File "venv/lib/python3.8/site-packages/anvil_consortium_manager/views.py", line 1225, in run_audit
    self.audit_results = models.ManagedGroup.anvil_audit()
  File "venv/lib/python3.8/site-packages/anvil_consortium_manager/models.py", line 733, in anvil_audit
    if not group.anvil_audit_membership().ok():
  File "venv/lib/python3.8/site-packages/anvil_consortium_manager/models.py", line 618, in anvil_audit_membership
    admins_in_anvil.remove(
ValueError: list.remove(x): x not in list