Fixed testdummy ticket output

src/tests/testdummy/ticketoutput.py

@@ -1,7 +1,5 @@
 import logging
 
-from django.http import HttpResponse
-
 from pretix.base.ticketoutput import BaseTicketOutput
 
 logger = logging.getLogger('tests.testdummy.ticketoutput')
@@ -13,6 +11,5 @@ class DummyTicketOutput(BaseTicketOutput):
     download_button_text = 'Download test file'
     download_button_icon = 'fa-print'
 
-    def generate(self, request, order):
-        response = HttpResponse(order.identity, content_type='text/plain')
-        return response
+    def generate(self, order):
+        return 'test.txt', 'text/plain', order.identity