date_format with "\n" as pattern has different behavior with MySQL

[lzmhhh123]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(dt datetime);

explain select * from t where dt <= date_format('2022-02-09', '%Y-%m-%d 16:33:00');

explain select * from t where dt <= date_format('2022-02-09', '%Y-%m-%d
16:33:00');

2. What did you expect to see? (Required)

The selection condition of execution plan in both sqls are le(test.t.dt, 2022-02-09 16:33:00.000000)

3. What did you see instead (Required)

The second is le(test.t.dt, NULL)

4. What is your TiDB version? (Required)

4.0, 5.0, 5.1, and older 5.1 versions.