fixed undeterministic RollingAppenderDirectCronTest

[rjuare8]

Stabilize RollingAppenderDirectCronTest by waiting for rolled file content and relaxing rollover timeout
Addresses #3046.

Important

Base your changes on 2.x branch if you are targeting Log4j 2; use main otherwise.

This PR hardens RollingAppenderDirectCronTest against timing races observed with cron-based rollovers. In practice, rolloverComplete(...) can fire before the first write to the newly rolled file has reached disk, causing the test to intermittently assert on an empty file. Under scheduler jitter, the test could also time out while waiting for a rollover.

What changed (test-only)

• In rolloverComplete(...), wait briefly until the rolled file exists and has non-zero length before asserting its contents:

  waitAtMost(2, TimeUnit.SECONDS).until(() -> Files.exists(path) && Files.size(path) > 0);

Why

• With CronTriggeringPolicy, the rollover completion callback may run before any event for the new time window is flushed to disk. The test previously asserted isNotEmpty() immediately and could race with IO, leading to flakiness (see RollingAppenderDirectCronTest.testAppender(LoggerContext, RollingFileAppender) is unreliable #3046).

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