Allow "default" bots to see mentions on all streams.

This change allows normal bots to get UserMessage rows when
they are mentioned on a stream, even if they are not actually
subscribed to the stream.

Fixes #7140.

zerver/tests/test_users.py

@@ -409,6 +409,7 @@ class RecipientInfoTest(ZulipTestCase):
             stream_push_user_ids={hamlet.id},
             um_eligible_user_ids=all_user_ids,
             long_term_idle_user_ids=set(),
+            default_bot_user_ids=set(),
             service_bot_tuples=[],
         )
 
@@ -451,6 +452,25 @@ class RecipientInfoTest(ZulipTestCase):
             (service_bot.id, UserProfile.EMBEDDED_BOT),
         ])
 
+        # Add a normal bot.
+        normal_bot = do_create_user(
+            email='normal-bot@zulip.com',
+            password='',
+            realm=realm,
+            full_name='',
+            short_name='',
+            active=True,
+            bot_type=UserProfile.DEFAULT_BOT,
+        )
+
+        info = get_recipient_info(
+            recipient=recipient,
+            sender_id=hamlet.id,
+            stream_topic=stream_topic,
+            possibly_mentioned_user_ids={service_bot.id, normal_bot.id}
+        )
+        self.assertEqual(info['default_bot_user_ids'], {normal_bot.id})
+
 class BulkUsersTest(ZulipTestCase):
     def test_client_gravatar_option(self):
         # type: () -> None