[CI] ReindexDatastreamIndexTransportActionIT testCustomReindexPipeline failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #6208 / ubuntu-2404-aarch64_checkpart2_platform-support-arm
• elasticsearch-periodic-platform-support #6201 / ubuntu-2404_platform-support-unix

Reproduction Line:

./gradlew ":x-pack:plugin:migrate:internalClusterTest" --tests "org.elasticsearch.xpack.migrate.action.ReindexDatastreamIndexTransportActionIT.testCustomReindexPipeline" -Dtests.seed=515C8704568845FC -Dtests.locale=ml-IN -Dtests.timezone=Pacific/Truk -Druntime.java=23

Applicable branches:
8.18

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: All incoming requests on node [node_s5] should have finished. Expected 0 bytes for requests in-flight but got 298 bytes; pending tasks [[{
  "node" : "node_s5",
  "id" : 15,
  "type" : "persistent",
  "action" : "health-node[c]",
  "status" : {
    "state" : "STARTED"
  },
  "description" : "id=health-node",
  "start_time" : "2025-02-05T21:58:24.738Z",
  "start_time_in_millis" : 1738792704738,
  "running_time" : "7.8m",
  "running_time_in_nanos" : 472504772695,
  "cancellable" : true,
  "cancelled" : false,
  "parent_task_id" : "cluster:2",
  "headers" : { }
}]]

Issue Reasons:

• [8.18] 2 failures in test testCustomReindexPipeline (2.0% fail rate in 99 executions)
• [8.18] 2 failures in pipeline elasticsearch-periodic-platform-support (66.7% 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/es-data-management (Team:Data Management)

[parkertimmins]

Fixed by #122274