[CI] ServerSentEventsRestActionListenerTests testOnFailure failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #11401 / sles-15_platform-support-unix
• elasticsearch-periodic-platform-support #11397 / opensuse-leap-15_platform-support-unix
• elasticsearch-periodic-platform-support #11397 / sles-15_platform-support-unix
• elasticsearch-periodic-platform-support #11397 / rhel-9_platform-support-unix
• elasticsearch-periodic-platform-support #11397 / ubuntu-2404-aarch64_checkpart2_platform-support-arm
• elasticsearch-periodic-platform-support #11393 / almalinux-9_platform-support-unix
• elasticsearch-periodic-platform-support #11393 / almalinux-8-aarch64_checkpart2_platform-support-arm

Reproduction Line:

./gradlew ":x-pack:plugin:inference:internalClusterTest" --tests "org.elasticsearch.xpack.inference.rest.ServerSentEventsRestActionListenerTests.testOnFailure" -Dtests.seed=9EBD735F277DA0BC -Dtests.locale=ga-Latn-IE -Dtests.timezone=Africa/Bamako -Druntime.java=25

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: 
Expected: an empty collection
     but: <[LEAK: resource was not cleaned up before it was garbage-collected.
Recent access records: 
#1:
	in [elasticsearch[node_s_0][system_read][T#1]][testStore_OverwritesConfiguration_WhenItAlreadyExists]
	org.elasticsearch.action.search.SearchResponseSections.close(SearchResponseSections.java:100)
	org.elasticsearch.core.Releasables.close(Releasables.java:39)
	org.elasticsearch.core.Releasables.closeExpectNoException(Releasables.java:72)
	org.elasticsearch.action.ActionListenerImplementations$2.run(ActionListenerImplementations.java:51)
	org.elasticsearch.action.ActionListener$1.onResponse(ActionListener.java:218)
	org.elasticsearch.action.ActionListener$3.onResponse(ActionListener.java:413)
	org.elasticsearch.action.support.SubscribableListener$SuccessResult.complete(SubscribableListener.java:423)
	org.elasticsearch.action.support.SubscribableListener.tryComplete(SubscribableListener.java:343)
	org.elasticsearch.action.sup
[truncated]

Issue Reasons:

• [main] 2 consecutive failures in step sles-15_platform-support-unix
• [main] 7 failures in test testOnFailure (5.1% fail rate in 136 executions)
• [main] 2 failures in step sles-15_platform-support-unix (66.7% fail rate in 3 executions)
• [main] 3 failures in pipeline elasticsearch-periodic-platform-support (100.0% fail rate in 3 executions)

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

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[jonathan-buttner]

#137839