AttributeError in MultiAuthenticator

[cgawron]

This bug relates to the dev environment!

@DeepCowProductions

[E 2023-04-24 18:12:06.284 JupyterHub web:1798] Uncaught exception GET /jupyterhub-dev/hub/login?next=%2Fjupyterhub-dev%2Fhub%2F (178.203.205.144)
    HTTPServerRequest(protocol='http', host='www.ki.fh-swf.de', method='GET', uri='/jupyterhub-dev/hub/login?next=%2Fjupyterhub-dev%2Fhub%2F', version='HTTP/1.1', remote_ip='178.203.205.144')
    Traceback (most recent call last):
      File "/usr/local/lib/python3.9/site-packages/tornado/web.py", line 1713, in _execute
        result = await result
      File "/usr/local/lib/python3.9/site-packages/jupyterhub/handlers/login.py", line 142, in get
        self.finish(await self._render(username=username))
      File "/usr/local/lib/python3.9/site-packages/jupyterhub/handlers/login.py", line 105, in _render
        self.authenticator.get_custom_html(self.hub.base_url)
      File "/usr/local/lib/python3.9/site-packages/multiauthenticator/multiauthenticator.py", line 42, in get_custom_html
        print(authenticator.__dict__)
    AttributeError: 'dict' object has no attribute '__dict__'

[DeepCowProductions]

fixed.