`ADDTIME` returns datetime instead of time

## 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 ADDTIME('2023-01-01', '12:34:56');
+-----------------------------------+
| ADDTIME('2023-01-01', '12:34:56') |
+-----------------------------------+
| 12:55:19 |
+-----------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> SELECT ADDTIME('2023-01-01', '237:00:00');
+------------------------------------+
| ADDTIME('2023-01-01', '237:00:00') |
+------------------------------------+
| 237:20:23 |
+------------------------------------+
1 row in set, 1 warning (0.00 sec)
```

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

```
mysql> SELECT ADDTIME('2023-01-01', '12:34:56');
+-----------------------------------+
| ADDTIME('2023-01-01', '12:34:56') |
+-----------------------------------+
| 2023-01-01 12:34:56 |
+-----------------------------------+
1 row in set (0.01 sec)

mysql> SELECT ADDTIME('2023-01-01', '237:00:00');
+------------------------------------+
| ADDTIME('2023-01-01', '237:00:00') |
+------------------------------------+
| 2023-01-10 21:00:00 |
+------------------------------------+
1 row in set (0.00 sec)
```

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