fix 404 for adding

fix 404 after the co-speaker press accept/decline during reviewing stage, which "SLUG.proposals.editable" is false.

Author: SivanYeh

src/proposals/views/mixins.py

@@ -25,8 +25,6 @@ def can_edit(self):
         return reg.get(f'{settings.CONFERENCE_DEFAULT_SLUG}.proposals.editable', False)
 
     def dispatch(self, request, *args, **kwargs):
-        if not self.can_edit():
-            raise Http404
         return super().dispatch(request, *args, **kwargs)