Fix serverless failure

Author: ioanatia

x-pack/plugin/esql/qa/testFixtures/src/main/resources/fork.csv-spec

@@ -114,7 +114,7 @@ fork2         | 6.093784261960139E18  | 2           | all we have to decide is w
 ;
 
 forkWithEvals
-required_capability: fork
+required_capability: fork_v2
 
 FROM employees
 | FORK (WHERE emp_no == 10048 OR emp_no == 10081 | EVAL x = "abc" | EVAL y = 1)
@@ -131,7 +131,7 @@ fork2         | 10087          | def       | null      | 2
 ;
 
 forkWithStats
-required_capability: fork
+required_capability: fork_v2
 
 FROM employees
 | FORK (WHERE emp_no == 10048 OR emp_no == 10081)
@@ -152,7 +152,7 @@ fork4         | null           | 100    | 10001     | null
 ;
 
 forkWithDissect
-required_capability: fork
+required_capability: fork_v2
 
 FROM employees
 | WHERE emp_no == 10048 OR emp_no == 10081
@@ -172,7 +172,7 @@ fork2         | 10081          | Rosen     | 10081     | null      | Zhongwei
 ;
 
 forkWithMixOfCommands
-required_capability: fork
+required_capability: fork_v2
 
 FROM employees
 | WHERE emp_no == 10048 OR emp_no == 10081

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -964,7 +964,12 @@ public enum Cap {
         /**
          * Support max_over_time aggregation
          */
-        MAX_OVER_TIME(Build.current().isSnapshot());
+        MAX_OVER_TIME(Build.current().isSnapshot()),
+
+        /**
+         * Support STATS/EVAL/DISSECT in Fork branches
+         */
+        FORK_V2(Build.current().isSnapshot());
 
         private final boolean enabled;