Fix losing incoming EDUs if debug logging enabled (#11890)

* Fix losing incoming EDUs if debug logging enabled

Fixes #11889. Homeservers should only be affected if the
`synapse.8631_debug` logger was enabled for DEBUG mode.

I am not sure if this merits a bugfix release: I think the logging can
be disabled in config if anyone is affected? But it is still pretty bad.

changelog.d/11890.bugfix

@@ -0,0 +1 @@
+Fix a bug introduced in Synapse 1.51.0rc1 where incoming federation transactions containing at least one EDU would be dropped if debug logging was enabled for `synapse.8631_debug`.

synapse/federation/transport/server/federation.py

@@ -109,11 +109,11 @@ class FederationSendServlet(BaseFederationServerServlet):
             )
 
             if issue_8631_logger.isEnabledFor(logging.DEBUG):
-                DEVICE_UPDATE_EDUS = {"m.device_list_update", "m.signing_key_update"}
+                DEVICE_UPDATE_EDUS = ["m.device_list_update", "m.signing_key_update"]
                 device_list_updates = [
                     edu.content
                     for edu in transaction_data.get("edus", [])
-                    if edu.edu_type in DEVICE_UPDATE_EDUS
+                    if edu.get("edu_type") in DEVICE_UPDATE_EDUS
                 ]
                 if device_list_updates:
                     issue_8631_logger.debug(