`MINUTE` cannot return correct minutes for truncated value

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 MINUTE('12:30:00+05:00');
+--------------------------+
| MINUTE('12:30:00+05:00') |
+--------------------------+
|                       30 |
+--------------------------+
1 row in set, 1 warning (0.02 sec)

mysql> show warnings;
+---------+------+--------------------------------------------------+
| Level   | Code | Message                                          |
+---------+------+--------------------------------------------------+
| Warning | 1292 | Truncated incorrect time value: '12:30:00+05:00' |
+---------+------+--------------------------------------------------+
1 row in set (0.06 sec)

3. What did you see instead (Required)

mysql> SELECT MINUTE('12:30:00+05:00');
+--------------------------+
| MINUTE('12:30:00+05:00') |
+--------------------------+
|                     NULL |
+--------------------------+
1 row in set, 1 warning (0.01 sec)

mysql> show warnings;
+---------+------+--------------------------------------------------+
| Level   | Code | Message                                          |
+---------+------+--------------------------------------------------+
| Warning | 1292 | Truncated incorrect time value: '12:30:00+05:00' |
+---------+------+--------------------------------------------------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

Start by reproducing the SELECT MINUTE('12:30:00+05:00') query and compare its result and warning with the expected output in the report. Trace the MINUTE expression's handling of the truncated time value, then add coverage showing that the function returns 30 while preserving the warning.