[SPARK-21516][SQL][TEST] Overriding afterEach() in DatasetCacheSuite must call super.afterEach()

## What changes were proposed in this pull request?

This PR ensures to call `super.afterEach()` in overriding `afterEach()` method in `DatasetCacheSuite`. When we override `afterEach()` method in Testsuite, we have to call `super.afterEach()`.

This is a follow-up of #18719 and SPARK-21512.

## How was this patch tested?

Used the existing test suite

Author: Kazuaki Ishizaki <ishizaki@jp.ibm.com>

Closes #18721 from kiszk/SPARK-21516.