Generics for `ObservableDeferred` (#10491)

Now that `Deferred` is a generic class, let's update `ObeservableDeferred` to
follow suit.

1 files changed, 3 insertions, 1 deletions

diff --git a/synapse/storage/persist_events.py b/synapse/storage/persist_events.py

index a39877f0d5..0e8270746d 100644
--- a/synapse/storage/persist_events.py
+++ b/synapse/storage/persist_events.py
@@ -170,7 +170,9 @@ class _EventPeristenceQueue(Generic[_PersistResult]):
             end_item = queue[-1]
         else:
             # need to make a new queue item
-            deferred = ObservableDeferred(defer.Deferred(), consumeErrors=True)
+            deferred: ObservableDeferred[_PersistResult] = ObservableDeferred(
+                defer.Deferred(), consumeErrors=True
+            )
 
             end_item = _EventPersistQueueItem(
                 events_and_contexts=[],