Cancelling translation process not possible

[timobrembeck]

Describe the Bug

When a page is currently in translation, its not possible to cancel this process anymore.

Steps to Reproduce

1. Go to page tree
2. Export page as xliff
3. Open page form that is in translation
4. Click on "Abort translation process"

Expected Behavior

The process should be aborted and the UI should be updated

Actual Behavior

Nothing happens and the ajax view returns a 500 error code

Additional Information

Traceback

Feb 15 01:15:50 ERROR   django.request - Internal Server Error: /ajax/nuernberg/post_translation_state
Traceback (most recent call last):
File "/opt/integreat-cms/.venv/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
  response = get_response(request)
File "/opt/integreat-cms/.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 "/opt/integreat-cms/.venv/lib/python3.8/site-packages/django/views/decorators/http.py", line 40, in inner
  return func(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.8/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
  return view_func(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.8/site-packages/integreat_cms/cms/decorators.py", line 112, in wrap
  return function(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.8/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
  return view_func(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.8/site-packages/integreat_cms/cms/views/pages/page_actions.py", line 395, in post_translation_state_ajax
  page_translation = page.get_translation(target_language.slug)
AttributeError: 'str' object has no attribute 'slug'