Use proper background task for async event handlers

Author: tulir

mautrix/client/syncer.py

@@ -34,6 +34,7 @@
     ToDeviceEvent,
     UserID,
 )
+from mautrix.util import background_task
 from mautrix.util.logging import TraceLogger
 
 from . import dispatcher
@@ -248,9 +249,10 @@ def dispatch_manual_event(
             handlers = self.global_event_handlers + handlers
         tasks = []
         for handler, wait_sync in handlers:
-            task = asyncio.create_task(self._catch_errors(handler, data))
             if force_synchronous or wait_sync:
-                tasks.append(task)
+                tasks.append(asyncio.create_task(self._catch_errors(handler, data)))
+            else:
+                background_task.create(self._catch_errors(handler, data))
         return tasks
 
     async def run_internal_event(