models: Add `is_announcement_only` to Stream.to_dict().

zerver/models.py

@@ -987,6 +987,7 @@ class Stream(models.Model):
             stream_id=self.id,
             description=self.description,
             invite_only=self.invite_only,
+            is_announcement_only=self.is_announcement_only,
             history_public_to_subscribers=self.history_public_to_subscribers
         )
 

zerver/tests/test_events.py

@@ -1123,6 +1123,7 @@ class EventsRegisterTest(ZulipTestCase):
                 ('streams', check_list(check_dict_only([
                     ('description', check_string),
                     ('invite_only', check_bool),
+                    ('is_announcement_only', check_bool),
                     ('name', check_string),
                     ('stream_id', check_int),
                     ('history_public_to_subscribers', check_bool)]))),