[CI] CrossClusterSearchUnavailableClusterIT testSkipUnavailableDependsOnSeeds failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic #6738 / openjdk17_checkpart1_java-fips-matrix
• elasticsearch-periodic #6703 / openjdk17_checkpart1_java-fips-matrix

Reproduction Line:

./gradlew ":qa:ccs-unavailable-clusters:javaRestTest" --tests "org.elasticsearch.search.CrossClusterSearchUnavailableClusterIT.testSkipUnavailableDependsOnSeeds" -Dtests.seed=8621B408D6E00BB2 -Dtests.locale=is-Latn-IS -Dtests.timezone=America/Montserrat -Druntime.java=17 -Dtests.fips.enabled=true

Applicable branches:
8.x

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[node0][transport_worker][T#12]][testSearchSkipUnavailable]
	org.elasticsearch.transport.OutboundHandler.lambda$sendResponse$1(OutboundHandler.java:158)
	org.elasticsearch.core.IOUtils.close(IOUtils.java:71)
	org.elasticsearch.core.IOUtils.close(IOUtils.java:87)
	org.elasticsearch.core.IOUtils.close(IOUtils.java:63)
	org.elasticsearch.core.Releasables.close(Releasables.java:73)
	org.elasticsearch.core.Releasables.close(Releasables.java:41)
	org.elasticsearch.core.Releasables$3.close(Releasables.java:129)
	org.elasticsearch.action.ActionListener$1.onResponse(ActionListener.java:217)
	org.elasticsearch.transport.OutboundHandler$1.onResponse(OutboundHandler.java:257)
	org.elasticsearch.transport.OutboundHandler$1.onResponse(OutboundHandler.java:253)
	org.elasticsearch.transport.netty4.Netty4Utils.lambda$addLis
[truncated]

Issue Reasons:

• [8.x] 2 failures in test testSkipUnavailableDependsOnSeeds (1.3% fail rate in 159 executions)
• [8.x] 2 failures in step openjdk17_checkpart1_java-fips-matrix (33.3% fail rate in 6 executions)
• [8.x] 2 failures in pipeline elasticsearch-periodic (33.3% fail rate in 6 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)