[CI] MultiClusterSpecIT class failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-intake #18605 / 8.19.0_bwc-snapshots
• elasticsearch-intake #18608 / 9.0.0_bwc-snapshots
• elasticsearch-intake #18607 / 9.0.0_bwc-snapshots
• elasticsearch-intake #18606 / 9.0.0_bwc-snapshots
• elasticsearch-pull-request #58629 / 8.19.0_bwc-snapshots
• elasticsearch-pull-request #58629 / 9.0.0_bwc-snapshots
• elasticsearch-intake #18605 / 9.0.0_bwc-snapshots
• elasticsearch-pull-request #58628 / 8.19.0_bwc-snapshots
• elasticsearch-pull-request #58628 / 9.0.0_bwc-snapshots
• elasticsearch-pull-request #58627 / 8.19.0_bwc-snapshots

Reproduction Line:

./gradlew ":x-pack:plugin:esql:qa:server:multi-clusters:v8.19.0#oldToNew" -Dtests.class="org.elasticsearch.xpack.esql.ccq.MultiClusterSpecIT" -Dtests.method="test {fork.ForkWithCommonPrefilter}" -Dtests.seed=B71C534A60B8FC24 -Dtests.bwc=true -Dtests.locale=hi-Deva-IN -Dtests.timezone=America/North_Dakota/Center -Druntime.java=23

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

org.elasticsearch.client.ResponseException: method [POST], host [http://[::1]:39681], URI [/_query?pretty=true&error_trace=true], status line [HTTP/1.1 400 Bad Request]
¿eerror¿jroot_cause�¿dtypeqparsing_exceptionfreasonxáline 3:3: mismatched input 'FORK' expecting {'dissect', 'drop', 'enrich', 'eval', 'grok', 'keep', 'limit', 'mv_expand', 'rename', 'sort', 'stats', 'where', 'lookup', DEV_INLINESTATS, DEV_LOOKUP, DEV_JOIN_LEFT, DEV_JOIN_RIGHT}kstack_tracey6org.elasticsearch.xpack.esql.parser.ParsingException: line 3:3: mismatched input 'FORK' expecting {'dissect', 'drop', 'enrich', 'eval', 'grok', 'keep', 'limit', 'mv_expand', 'rename', 'sort', 'stats', 'where', 'lookup', DEV_INLINESTATS, DEV_LOOKUP, DEV_JOIN_LEFT, DEV_JOIN_RIGHT}
	at org.elasticsearch.xpack.esql.parser.EsqlParser$1.syntaxError(EsqlParser.java:149)
	at org.antlr.v4.runtime.ProxyErrorListener.syntaxError(ProxyErrorListener.java:41)
	at org.antlr.v4.runtime.Parser.notifyErrorListeners(Parser.java:544)
	at org.antlr.v4.r
[truncated]

Issue Reasons:

• [main] 35 failures in class org.elasticsearch.xpack.esql.ccq.MultiClusterSpecIT (3.5% fail rate in 1000 executions)
• [main] 19 failures in step 8.19.0_bwc-snapshots (16.0% fail rate in 119 executions)
• [main] 15 failures in step 9.0.0_bwc-snapshots (12.1% fail rate in 124 executions)
• [main] 7 failures in pipeline elasticsearch-intake (15.2% fail rate in 46 executions)
• [main] 15 failures in pipeline elasticsearch-pull-request (17.9% fail rate in 84 executions)

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

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[alex-spies]

I think this should be addressed, c.f. #123136