[9.3] Fix flaky ThreadPoolMergeSchedulerStressTestIT (#139819)#140345

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elasticsearchmachine merged 3 commits intoelastic:9.3from

burqen:backport/9.3/pr-139819

Jan 9, 2026

Commits on Jan 8, 2026

Commits on Jan 9, 2026

Merge remote-tracking branch 'upstream/9.3' into backport/9.3/pr-139819
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