### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

all

### Problem Description

Do this

### Steps to Reproduce

```
rm /tmp/evil
for a in {0..9}; do
   for b in {0..9}; do
      echo '{"index": {}}' >> /tmp/evil
      echo '{"a": '$a', "b": '$b'}' >> /tmp/evil
   done
done
echo >> /tmp/evil

curl -uelastic:password -XDELETE localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPUT localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_bulk --data-binary @/tmp/evil
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_forcemerge?max_num_segments=1
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_refresh

curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/_esql?pretty -d'{
   "query": "FROM test | STATS MAX(a) BY a, b | KEEP a"
}'
```

### Logs (if relevant)

_No response_
x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/CsvTestUtils.java
return switch (elementType) {
                case INT -> INTEGER;
                case LONG -> LONG;
                case DOUBLE -> DOUBLE;
                case NULL -> NULL;
                case BYTES_REF -> KEYWORD;
                case BOOLEAN -> BOOLEAN;
                case DOC -> throw new IllegalArgumentException("can't assert on doc blocks");
                case UNKNOWN -> throw new IllegalArgumentException("Unknown block types cannot be handled");
            };
        }
        Object convert(String value) {
            if (value == null) {
                return null;
            }
            return converter.apply(value);
        }
        Class<?> clazz() {
            return clazz;
        }
        public Comparator<Object> comparator() {
            return comparator;
        }
    }
    record ActualResults(
        List<String> columnNames,
        List<Type> columnTypes,
        List<String> dataTypes,
        List<Page> pages,
        Map<String, List<String>> responseHeaders