Ignore test testDLQWriterFlusherRemovesExpiredSegmentWhenCurrentHeadSegmentIsEmpty on WIndows

[andsel]

Given that the test DeadLetterQueueWriterAgeRetentionTest .testDLQWriterFlusherRemovesExpiredSegmentWhenCurrentHeadSegmentIsEmpty fails only on Windows platform, ignore selectively the test for that environment.
For example, with JUnit4 we could leverage the Assume and at the start of the test:

@Test
public void testSomething() {
    assumeThat(getOsName(), is(not("Windows")));
    // testing code
}

[dliappis]

In case it could be a useful data point, wanted to share that we don't observe Windows failures with the 7.17 branch: https://buildkite.com/elastic/logstash-exhaustive-tests-pipeline/builds?branch=7.17

[andsel]

Thanks @dliappis for checking it, I think it's due to the fact that the age retention policy feature (#14255) and tests were introduced in 8.4.0