Update CompletableConcatTest.java

Author: akarnokd

src/test/java/io/reactivex/rxjava3/internal/operators/completable/CompletableConcatTest.java

@@ -54,7 +54,7 @@ public void subscribe(Subscriber<? super Completable> s) {
             .test()
             .assertFailure(QueueOverflowException.class);
 
-            TestHelper.assertError(errors, 0, MissingBackpressureException.class);
+            TestHelper.assertError(errors, 0, QueueOverflowException.class);
         } finally {
             RxJavaPlugins.reset();
         }