`SUBTIME` should return `TIME` even if the argument looks like `DATETIME`

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

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

```

mysql> SELECT SUBTIME('2024-03-01', '24:00:00');
+-----------------------------------+
| SUBTIME('2024-03-01', '24:00:00') |
+-----------------------------------+
| -23:39:36 |
+-----------------------------------+
1 row in set, 1 warning (0.01 sec)

mysql> SELECT SUBTIME('2024-02-29', '1 12:00:00');
+-------------------------------------+
| SUBTIME('2024-02-29', '1 12:00:00') |
+-------------------------------------+
| -35:39:36 |
+-------------------------------------+
1 row in set, 1 warning (0.01 sec)

mysql> SELECT SUBTIME('2024-02-29', '1 00:00:00');
+-------------------------------------+
| SUBTIME('2024-02-29', '1 00:00:00') |
+-------------------------------------+
| -23:39:36 |
+-------------------------------------+
1 row in set, 1 warning (0.00 sec)
```

### 3. What did you see instead (Required)

```

mysql> SELECT SUBTIME('2024-03-01', '24:00:00');
+-----------------------------------+
| SUBTIME('2024-03-01', '24:00:00') |
+-----------------------------------+
| 2024-02-29 00:00:00 |
+-----------------------------------+
1 row in set (0.00 sec)

mysql> SELECT SUBTIME('2024-02-29', '1 12:00:00');
+-------------------------------------+
| SUBTIME('2024-02-29', '1 12:00:00') |
+-------------------------------------+
| 2024-02-27 12:00:00 |
+-------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT SUBTIME('2024-02-29', '1 00:00:00');
+-------------------------------------+
| SUBTIME('2024-02-29', '1 00:00:00') |
+-------------------------------------+
| 2024-02-28 00:00:00 |
+-------------------------------------+
1 row in set (0.00 sec)
```

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