fix(pubsub): use GRPCConnPool option for subscriber client (#2624)

diff --git a/pubsub/pubsub.go b/pubsub/pubsub.go
index a14f669..d73adcf 100644
--- a/pubsub/pubsub.go
+++ b/pubsub/pubsub.go
@@ -80,7 +80,7 @@
 	if err != nil {
 		return nil, fmt.Errorf("pubsub: %v", err)
 	}
-	subc, err := vkit.NewSubscriberClient(ctx, option.WithGRPCConn(pubc.Connection()))
+	subc, err := vkit.NewSubscriberClient(ctx, o...)
 	if err != nil {
 		// Should never happen, since we are passing in the connection.
 		// If it does, we cannot close, because the user may have passed in their