Use newer action form API from core

aleksis/apps/tezor/views.py

@@ -151,9 +151,7 @@ class InvoiceGroupDetailView(PermissionRequiredMixin, DetailView):
     def post(self, request, *args, **kwargs):
         r = super().get(request, *args, **kwargs)
         if self.invoices_action_form.is_valid():
-            action = self.invoices_action_form._get_actions_dict()[
-                self.invoices_action_form.cleaned_data["action"]
-            ]
+            action = self.invoices_action_form.cleaned_data["action"]
             if request.user.has_perm(action.permission):
                 self.invoices_action_form.execute()
         return r