pubsub: use staging endpoint for filtering test

Fixes #2388
Updates #2390

Change-Id: I6e4af2972e8efa0937899a9f6bcc33dbb9f501c0
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/57090
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Seth Hollyman <shollyman@google.com>
Reviewed-by: Cody Oss <codyoss@google.com>
diff --git a/pubsub/integration_test.go b/pubsub/integration_test.go
index 7fb403e..180f883 100644
--- a/pubsub/integration_test.go
+++ b/pubsub/integration_test.go
@@ -1533,7 +1533,10 @@
 func TestIntegration_Filter_CreateSubscription(t *testing.T) {
 	t.Parallel()
 	ctx := context.Background()
-	client := integrationTestClient(ctx, t)
+	// TODO(hongalex): Remove this once filtering is GA.
+	// https://github.com/googleapis/google-cloud-go/issues/2390
+	opts := withGRPCHeadersAssertion(t, option.WithEndpoint("staging-pubsub.sandbox.googleapis.com:443"))
+	client := integrationTestClient(ctx, t, opts...)
 	defer client.Close()
 
 	topic, err := client.CreateTopic(ctx, topicIDs.New())