Instable test: PostgresShutdownIT#shouldStopOnPostgresFastShutdown()

This one occassionally fails, e.g. see here: https://github.com/debezium/debezium/pull/2046/checks?check_run_id=1693680097

I think the last assertion (assertFalse(isStreamingRunning("postgres", TestHelper.TEST_SERVER));) should be in an Awaitility block.