[CI] ThreadPoolMergeExecutorServiceDiskSpaceTests testUnavailableBudgetBlocksNewMergeTasksFromStartingExecution failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic #8779 / openjdk23_checkpart1_java-matrix
• elasticsearch-periodic-platform-support #8794 / debian-12_platform-support-unix
• elasticsearch-periodic-platform-support #8794 / rhel-7_platform-support-unix
• elasticsearch-periodic #8773 / graalvm-ce17_checkpart1_java-matrix
• elasticsearch-periodic-platform-support #8788 / debian-11_platform-support-unix
• elasticsearch-periodic-platform-support #8782 / sles-12_platform-support-unix
• elasticsearch-periodic #8761 / openjdk21_checkpart1_java-matrix
• elasticsearch-periodic #8749 / openjdk17_checkpart1_java-matrix
• elasticsearch-periodic-platform-support #8764 / opensuse-leap-15_platform-support-unix
• elasticsearch-periodic-platform-support #8758 / windows-2025_checkpart1_platform-support-windows

Reproduction Line:

./gradlew ":server:test" --tests "org.elasticsearch.index.engine.ThreadPoolMergeExecutorServiceDiskSpaceTests.testUnavailableBudgetBlocksNewMergeTasksFromStartingExecution" -Dtests.seed=6739115B2A9F7E82 -Dtests.locale=de-AT -Dtests.timezone=SystemV/CST6 -Druntime.java=23

Applicable branches: 8.19

Reproduces locally?: N/A

Failure History: See dashboard

Failure Message:

java.lang.AssertionError: 
Expected: is <true>
     but: was <false>

Issue Reasons:

• [8.19] 3 consecutive failures in test testUnavailableBudgetBlocksNewMergeTasksFromStartingExecution
• [8.19] 22 failures in test testUnavailableBudgetBlocksNewMergeTasksFromStartingExecution (3.4% fail rate in 638 executions)
• [8.19] 2 failures in step debian-12_platform-support-unix (13.3% fail rate in 15 executions)
• [8.19] 2 failures in step ubuntu-2404_platform-support-unix (14.3% fail rate in 14 executions)
• [8.19] 2 failures in step opensuse-leap-15_platform-support-unix (14.3% fail rate in 14 executions)
• [8.19] 4 failures in step part-1 (4.5% fail rate in 89 executions)
• [8.19] 5 failures in pipeline elasticsearch-periodic (33.3% fail rate in 15 executions)
• [8.19] 9 failures in pipeline elasticsearch-periodic-platform-support (60.0% fail rate in 15 executions)
• [8.19] 5 failures in pipeline elasticsearch-pull-request (5.8% fail rate in 86 executions)

Note: This issue was created using new test triage automation. Please report issues or feedback to es-delivery.