test flake: Prevent flaky test with less common id.

This fixes a test flake introduced here:

    317a2fff2a

We need a higher bogus bot owner id to prevent
flakes where our userid sequence gets to 100.  (Tests
aren't completely deterministic in what data you
use, since sequences don't get rolled back when
you roll back transactions.)

zerver/tests/test_bots.py

@@ -733,8 +733,9 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
         email = 'hambot-bot@zulip.testserver'
         profile = get_user('hambot-bot@zulip.testserver', get_realm('zulip'))
 
+        bad_bot_owner_id = 999999
         bot_info = {
-            'bot_owner_id': 100,
+            'bot_owner_id': bad_bot_owner_id,
         }
         result = self.client_patch("/json/bots/{}".format(self.get_bot_user(email).id), bot_info)
         self.assert_json_error(result, "Failed to change owner, no such user")