Decimal type fields cannot be resized or precision improved within the partition table

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
create table test(
id int not null primary key auto_increment,
cost decimal(10,0) default 0 not null
)engine = innodb
partition by hash(id)
PARTITIONS 4 ;

alter table test modify column cost decimal(20,4) default 0 not null;

### 2. What did you expect to see? (Required)
sql error : Unsupported modify column: table is partition table

### 3. What did you see instead (Required)
Change fields to decimal(20,4)

### 4. What is your TiDB version? (Required)
6.5.0 +