Fix EsqlActionIT.testGroupingStatsOnMissingFields in release tests (#130177)

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/EsqlActionIT.java

@@ -1680,6 +1680,7 @@ public class EsqlActionIT extends AbstractEsqlIntegTestCase {
     }
 
     public void testGroupingStatsOnMissingFields() {
+        assumeTrue("Pragmas are only allowed in snapshots", Build.current().isSnapshot());
         assertAcked(client().admin().indices().prepareCreate("missing_field_index").setMapping("data", "type=long"));
         long oneValue = between(1, 1000);
         indexDoc("missing_field_index", "1", "data", oneValue);