fix twisted import error

Author: H-Shay

tests/rest/client/test_media.py

@@ -29,7 +29,7 @@
 from twisted.internet.address import IPv4Address, IPv6Address
 from twisted.internet.error import DNSLookupError
 from twisted.internet.interfaces import IAddress, IResolutionReceiver
-from twisted.internet.testing import AccumulatingProtocol, MemoryReactor
+from twisted.test.proto_helpers import AccumulatingProtocol, MemoryReactor
 from twisted.web.resource import Resource
 
 from synapse.config.oembed import OEmbedEndpointConfig