AttributeError during DeepL translation

[timobrembeck]

Describe the Bug

The changes introduced in #2124 broke the existing DeepL features

Steps to Reproduce

1. Go to page form and save
2. Or go to event/location list and use automatic translation feature
3. See error

Expected Behavior

The translations should be updated automatically

Actual Behavior

An AttributeError appears

Additional Information

Traceback (page form)

Traceback (most recent call last):
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/core/handlers/exception.py", line 47, in inner
  response = get_response(request)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/core/handlers/base.py", line 181, in _get_response
  response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/views/generic/base.py", line 70, in view
  return self.dispatch(request, *args, **kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/utils/decorators.py", line 43, in _wrapper
  return bound_method(*args, **kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
  return view_func(request, *args, **kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/views/generic/base.py", line 98, in dispatch
  return handler(request, *args, **kwargs)
File "/usr/lib/python3.10/contextlib.py", line 79, in inner
  return func(*args, **kwds)
File "/home/timo/job/integreat/integreat-cms/integreat_cms/cms/views/pages/page_form_view.py", line 352, in post
  and machine_translation_form.is_valid()
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/forms/forms.py", line 175, in is_valid
  return self.is_bound and not self.errors
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/forms/forms.py", line 170, in errors
  self.full_clean()
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/forms/forms.py", line 372, in full_clean
  self._clean_fields()
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/forms/forms.py", line 390, in _clean_fields
  value = field.clean(value)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/forms/models.py", line 1334, in clean
  return self.queryset.none()

Exception Type: AttributeError at /augsburg/pages/de/1/edit/
Exception Value: 'NoneType' object has no attribute 'none'

Traceback (event/location list)

Traceback (most recent call last):
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/core/handlers/exception.py", line 47, in inner
  response = get_response(request)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/core/handlers/base.py", line 181, in _get_response
  response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/views/generic/base.py", line 70, in view
  return self.dispatch(request, *args, **kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/contrib/auth/mixins.py", line 104, in dispatch
  return super().dispatch(request, *args, **kwargs)
File "/home/timo/job/integreat/integreat-cms/.venv/lib/python3.10/site-packages/django/views/generic/base.py", line 98, in dispatch
  return handler(request, *args, **kwargs)
File "/home/timo/job/integreat/integreat-cms/integreat_cms/cms/views/bulk_action_views.py", line 133, in post
  if deepl.check_availability(request, kwargs.get("language_slug")):
File "/home/timo/job/integreat/integreat-cms/integreat_cms/deepl_api/utils.py", line 44, in check_availability
  source_language = request.region.get_source_language(target_language.slug)