fix: flaky TestCancelOverridesPendingWants (#1016)

added 10ms delay before AddCancels to fix race condition.

after collectMessages returns, the queue's goroutine might still be
marking items as "sent". without this delay, AddCancels might not see
the CIDs as sent and won't create cancel messages, causing test timeout.

fixes CI failures with -race flag.

Author: lidel

bitswap/client/internal/messagequeue/messagequeue_test.go

@@ -356,15 +356,27 @@ func TestCancelOverridesPendingWants(t *testing.T) {
 	}
 
 	// Cancel the remaining want-blocks and want-haves
-	cancels = append(wantHaves, wantBlocks...)
+	// These CIDs were sent in the first message, so canceling them should
+	// generate cancel messages
+
+	// Small delay to avoid race condition: after collectMessages returns,
+	// the message has been sent to the channel, but the queue's goroutine
+	// might still be marking items as "sent". Without this delay, AddCancels
+	// might not find the CIDs in the sent list and won't generate cancel messages.
+	time.Sleep(10 * time.Millisecond)
+
+	cancels = []cid.Cid{wantBlocks[1], wantHaves[1]}
 	messageQueue.AddCancels(cancels)
 	messages = collectMessages(ctx, t, messagesSent, collectTimeout)
 
 	// The remaining 2 cancels should be sent to the network as they are for
 	// wants that were sent to the network
+	if len(messages) == 0 {
+		t.Fatal("Expected cancel messages but got none")
+	}
 	_, _, cl = filterWantTypes(messages[0])
 	if len(cl) != 2 {
-		t.Fatal("Expected 2 cancels")
+		t.Fatalf("Expected 2 cancels, got %d", len(cl))
 	}
 }