Fix off-by-one error reported in elastic#118051

Author: craigtaverner

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/esql/60_usage.yml

@@ -163,4 +163,4 @@ setup:
   - match: {esql.functions.cos: $functions_cos}
   - gt: {esql.functions.to_long: $functions_to_long}
   - match: {esql.functions.coalesce: $functions_coalesce}
-  - length: {esql.functions: 123} # check the "sister" test above for a likely update to the same esql.functions length check
+  - length: {esql.functions: 124} # check the "sister" test above for a likely update to the same esql.functions length check