Fix logcontext leak in http pusher test

tests/push/test_http.py

@@ -18,6 +18,7 @@ from mock import Mock
 from twisted.internet.defer import Deferred
 
 from synapse.rest.client.v1 import admin, login, room
+from synapse.util.logcontext import make_deferred_yieldable
 
 from tests.unittest import HomeserverTestCase
 
@@ -47,7 +48,7 @@ class HTTPPusherTests(HomeserverTestCase):
         def post_json_get_json(url, body):
             d = Deferred()
             self.push_attempts.append((d, url, body))
-            return d
+            return make_deferred_yieldable(d)
 
         m.post_json_get_json = post_json_get_json