Fix asan error in moqt_session_test.

PiperOrigin-RevId: 788033524

quiche/quic/moqt/moqt_session_test.cc

diff --git a/quiche/quic/moqt/moqt_session_test.cc b/quiche/quic/moqt/moqt_session_test.cc
index d801242..55e47dc 100644
--- a/quiche/quic/moqt/moqt_session_test.cc
+++ b/quiche/quic/moqt/moqt_session_test.cc
@@ -3046,6 +3046,7 @@
   EXPECT_TRUE(object_ready);
   EXPECT_TRUE(task->HasObject());
   EXPECT_FALSE(task->NeedsMorePayload());
+  task->SetObjectAvailableCallback(nullptr);
 }
 
 TEST_F(MoqtSessionTest, DeliveryTimeoutParameter) {