Partition table of TiDB doesn't support subpartition but is created successfully

[TonsnakeLin]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table if exists thash15;
CREATE TABLE thash15 (
    col1 INT NOT NULL,
    col2 INT NOT NULL,
    col3 INT NOT NULL,
    col4 INT NOT NULL,
    primary KEY (col1,col3)
)
PARTITION BY HASH(col1) PARTITIONS 4
SUBPARTITION BY HASH(col3) SUBPARTITIONS 2 

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

The table is not created and give an error that is "It is only possible to mix RANGE/LIST partitioning with HASH/KEY partitioning for subpartitioning"

3. What did you see instead (Required)

The table is created bu treated as normal table.

4. What is your TiDB version? (Required)

Release Version: v6.2.0-alpha-2066-g62e8709-dirty
Edition: Community
Git Commit Hash: 62e8709
Git Branch: key-partition
UTC Build Time: 2023-02-08 07:26:38
GoVersion: go1.19
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: tikv