Language menu issue

[marksweb]

Just looking at moving to cms rc3 and running versioning from master and I'm seeing the following when trying to edit a page;

  File "/Users/mwalker/Sites/consoles/.env/lib/python3.9/site-packages/cms/toolbar/toolbar.py", line 501, in _call_toolbar
    getattr(toolbar, func_name)()
  File "/Users/mwalker/Sites/consoles/.env/lib/python3.9/site-packages/djangocms_versioning/cms_toolbars.py", line 313, in populate
    self.override_language_menu()
  File "/Users/mwalker/Sites/consoles/.env/lib/python3.9/site-packages/djangocms_versioning/cms_toolbars.py", line 328, in override_language_menu
    for _item in copy(language_menu.items):
AttributeError: 'NoneType' object has no attribute 'items'

[fsbraun]

This happens when only one language is configured: django CMS does not offer the language menu any more (since there are no language actions). djangocms-versioning incorrectly assumes that a language menu exists.

The fix is here: #333 . Can you take a look and review?