list_signals fails with AttributeError: 'str' object has no attribute '_meta'

[edward-springload]

With Django 4.1.9 and Wagtail 4.2.3 list_signals is failing.

Traceback:

Traceback (most recent call last):
  File "/app/./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.11/site-packages/django/core/management/__init__.py", line 446, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.11/site-packages/django/core/management/__init__.py", line 440, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.11/site-packages/django/core/management/base.py", line 402, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.11/site-packages/django/core/management/base.py", line 448, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django_extensions/management/commands/list_signals.py", line 67, in handle
    verbose_name = force_str(key._meta.verbose_name)
                             ^^^^^^^^^
AttributeError: 'str' object has no attribute '_meta'

If I alter the code to print each key, the one which fails is the string '_unknown_'