[BUG] Flaky test - CacheStatsAPIIndicesRequestCacheIT.testNullLevels()

[peteralfonsi]

Describe the bug

CacheStatsAPIIndicesRequestCacheIT.testNullLevels() can fail. Example here.

Related component

Search:Performance

To Reproduce

REPRODUCE WITH: ./gradlew ':server:internalClusterTest' --tests "org.opensearch.indices.CacheStatsAPIIndicesRequestCacheIT" -Dtests.method="testNullLevels {p0={"opensearch.experimental.feature.pluggable.caching.enabled":"true"}}" -Dtests.seed=BEA24735BC98ED42 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=ar-EG -Dtests.timezone=Asia/Shanghai -Druntime.java=21

Expected behavior

The test should pass (the size of the resulting map should be 6, not 7).

Additional Details

No response