[CI] ReindexBasicTests testReindexIncludeVectors failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic #9272 / release-tests
• elasticsearch-periodic #9265 / release-tests
• elasticsearch-periodic #9251 / release-tests

Reproduction Line:

./gradlew ":modules:reindex:test" --tests "org.elasticsearch.reindex.ReindexBasicTests.testReindexIncludeVectors" -Dtests.seed=EA52D82CF19A49CE -Dbuild.snapshot=false -Dtests.jvm.argline="-Dbuild.snapshot=false" -Dlicense.key=x-pack/license-tools/src/test/resources/public.key -Dtests.locale=dyo-SN -Dtests.timezone=America/Panama -Druntime.java=24

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.IllegalArgumentException: unknown setting [index.mapping.synthetic_vectors] did you mean [index.mapping.synthetic_source_keep]?

Issue Reasons:

• [main] 3 consecutive failures in step release-tests
• [main] 3 failures in test testReindexIncludeVectors (1.3% fail rate in 237 executions)
• [main] 3 failures in step release-tests (100.0% fail rate in 3 executions)
• [main] 3 failures in pipeline elasticsearch-periodic (75.0% 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-search (Team:Search)