title: Django CreateView success message not shown
body: <p>I have a CreateView and an UpdateView with success messages in both. But, only the UpdateView success message works and the CreateView message isn't show. Why is this happening?       </p>
  
  <pre><code>from django.contrib.messages.views import SuccessMessageMixin
   class CreateRedirect (CreateView):
          model = MarketingRedirect
          template_name = 'marketing_redirect/create_redirect.html'
          success_url = reverse_lazy('backend_redirect')
          fields = ['redirect_from', 'redirect_to']
          success_message = "Redirect successfully created!"
  
  
      class EditRedirect(SuccessMessageMixin, UpdateView):
          model = MarketingRedirect
          fields = ['redirect_from', 'redirect_to']
          template_name = 'marketing_redirect/edit_redirect.html'
          context_object_name = 'redirect'
          success_url = reverse_lazy('backend_redirect')
          success_message = 'Review successfully updated'
  </code></pre>