Address more code review comments

Author: julian-elastic

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/PostOptimizationPhasePlanVerifier.java

@@ -55,6 +55,7 @@ private static void verifyOutputNotChanged(QueryPlan<?> optimizedPlan, List<Attr
         if (dataTypeEquals(expectedOutputAttributes, optimizedPlan.output()) == false) {
             // If the output level is empty we add a column called ProjectAwayColumns.ALL_FIELDS_PROJECTED
             // We will ignore such cases for output verification
+            // TODO: this special casing is required due to https://github.com/elastic/elasticsearch/issues/121741, remove when fixed.
             boolean hasProjectAwayColumns = optimizedPlan.output()
                 .stream()
                 .anyMatch(x -> x.name().equals(ProjectAwayColumns.ALL_FIELDS_PROJECTED));