[CI] SearchHitsTests testConcurrentSerialization failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #8308 / ubuntu-2404-aarch64_checkpart1_platform-support-arm
• elasticsearch-periodic-platform-support #8212 / ubuntu-2404-aarch64_checkpart1_platform-support-arm

Reproduction Line:

./gradlew ":server:test" --tests "org.elasticsearch.search.SearchHitsTests.testConcurrentSerialization" -Dtests.seed=B8E0357A2F81F936 -Dtests.locale=pcm -Dtests.timezone=Europe/Kiev -Druntime.java=24

Applicable branches:
8.19

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: 
Expected: <org.elasticsearch.search.SearchHits@25c71cba>
     but: was <org.elasticsearch.search.SearchHits@25c71cba>

Issue Reasons:

• [8.19] 2 failures in test testConcurrentSerialization (0.4% fail rate in 567 executions)
• [8.19] 2 failures in step ubuntu-2404-aarch64_checkpart1_platform-support-arm (11.8% fail rate in 17 executions)
• [8.19] 2 failures in pipeline elasticsearch-periodic-platform-support (11.8% fail rate in 17 executions)

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

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)

[elasticsearchmachine]

Pinging @elastic/es-search-foundations (Team:Search Foundations)