GcsSinkTaskGroupByTopicPartitionPropertiesTest.limited takes very long time

After upgrade to `google-cloud-nio:0.123.24` (and associated `google-cloud-storage:2.4.5`), `GcsSinkTaskGroupByTopicPartitionPropertiesTest.limited` started running very long time. It used to be a couple of minutes, but is unknown (I wan't patient enough to wait beyond 20 minutes).

Some crude profiling of [this line](https://github.com/aiven/gcs-connector-for-apache-kafka/blob/master/src/test/java/io/aiven/kafka/connect/common/grouper/GcsSinkTaskGroupByTopicPartitionPropertiesTest.java#L84)
```java
Instant started = Instant.now();
task.flush(null);
System.out.println(Duration.between(started, Instant.now()).toMillis());
```
shows that the time in `flush` grew about 10x.
No significant difference in profiles collected by `async-profiler` in `cpu` and `wall` modes.

The test will be disabled and should be enabled once this is fixed.