ES|QL: Skip FORK tests for CCS for now

[ioanatia]

We see a bunch of new failures for multi clusters

#127268
#127279
#127304
#127272

All these failures happened in the last 24h - most likely there are somehow related to #126705 which was merged last week.
However I am not sure why we have not seen these types of failures earlier.

Most likely all FORK related tests will fail with the same type of error for multi clusters - I haven't seen any for multi or single node tests.
I am skipping the FORK tests for multi clusters for now.

[carlosdelest]

I'm OK with this, but should we instead use muted-tests.yml and open an issue so we keep track of this?

[ioanatia]

I'm OK with this, but should we instead use muted-tests.yml and open an issue so we keep track of this?

I'm using the same pattern we have for INLINESTATS and unmapped fieds:

elasticsearch/x-pack/plugin/esql/qa/server/multi-clusters/src/javaRestTest/java/org/elasticsearch/xpack/esql/ccq/MultiClusterSpecIT.java

Lines 125 to 132 in a684e10

	assumeTrue("Test " + testName + " is skipped on " + oldVersion, isEnabled(testName, instructions, oldVersion));
	assumeFalse("INLINESTATS not yet supported in CCS", testCase.requiredCapabilities.contains(INLINESTATS.capabilityName()));
	assumeFalse("INLINESTATS not yet supported in CCS", testCase.requiredCapabilities.contains(INLINESTATS_V2.capabilityName()));
	assumeFalse("INLINESTATS not yet supported in CCS", testCase.requiredCapabilities.contains(JOIN_PLANNING_V1.capabilityName()));
	assumeFalse("INLINESTATS not yet supported in CCS", testCase.requiredCapabilities.contains(INLINESTATS_V5.capabilityName()));
	assumeFalse("LOOKUP JOIN not yet supported in CCS", testCase.requiredCapabilities.contains(JOIN_LOOKUP_V12.capabilityName()));
	// Unmapped fields require a coorect capability response from every cluster, which isn't currently implemented.
	assumeFalse("UNMAPPED FIELDS not yet supported in CCS", testCase.requiredCapabilities.contains(UNMAPPED_FIELDS.capabilityName()));

FORK might be used when testing RRF and RERANK (if I am not mistaken, there's a test for using RERANK with FORK and RRF). Until we figure out why CCS suddenly has flaky specs, I don't want to make it a requirement when adding a test that's using FORK that's not in the fork.csv-spec to mute it in muted-tests.yml.

Figuring out the CCS failures is tracked in #121950