[CI] RestCancellableNodeClientTests testConcurrentExecuteAndClose failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #9081 / almalinux-8-aarch64_platform-support-arm
• elasticsearch-periodic-platform-support #9059 / rhel-9_platform-support-unix

Reproduction Line:

./gradlew ':server:test' --tests "org.elasticsearch.rest.action.RestCancellableNodeClientTests.testConcurrentExecuteAndClose" -Dtests.seed=5D8A75F24A010EF6 -Dtests.locale=da -Dtests.timezone=Etc/GMT+0 -Druntime.java=22

Applicable branches:
7.17

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: expected:<25> but was:<26>

Issue Reasons:

• [7.17] 2 failures in test testConcurrentExecuteAndClose (1.5% fail rate in 136 executions)
• [7.17] 2 failures in pipeline elasticsearch-periodic-platform-support (50.0% fail rate in 4 executions)

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

[elasticsearchmachine]

Pinging @elastic/es-distributed-coordination (Team:Distributed Coordination)

[nicktindall]

I suspect this is due to the fact neither #128085 or #129294 are back-ported to 7.17

I was going to back-port them but realised that opens a can of worms because the fix for #128085 depends on things that didn't exist in 7.17

Marking as low risk because they're both test bugs