Downgrade warning on client disconnect to INFO (#7928)

Clients disconnecting before we finish processing the request happens from time
to time. We don't need to yell about it

synapse/http/site.py

@@ -215,9 +215,7 @@ class SynapseRequest(Request):
         # It's useful to log it here so that we can get an idea of when
         # the client disconnects.
         with PreserveLoggingContext(self.logcontext):
-            logger.warning(
-                "Error processing request %r: %s %s", self, reason.type, reason.value
-            )
+            logger.info("Connection from client lost before response was sent")
 
             if not self._is_processing:
                 self._finished_processing()