Merge pull request #2027 from matrix-org/rav/logcontext_leaks

synapse/app/appservice.py

synapse/app/client_reader.py

synapse/app/federation_reader.py

synapse/app/federation_sender.py

synapse/app/homeserver.py

synapse/app/media_repository.py

synapse/app/pusher.py

synapse/app/synchrotron.py

synapse/handlers/federation.py

synapse/storage/background_updates.py

synapse/util/logcontext.py

tests/util/test_log_context.py