STR_TO_DATE('2016_01 Monday', "%X_%V %W") doesn't work

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
SELECT STR_TO_DATE('2016_01 Monday', "%X_%V %W");
```

### 2. What did you expect to see? (Required)
results from mysql8
```
MySQL [fuzztest]> SELECT STR_TO_DATE('2016_01 Monday', "%X_%V %W");
+-------------------------------------------+
| STR_TO_DATE('2016_01 Monday', "%X_%V %W") |
+-------------------------------------------+
| 2016-01-04 |
+-------------------------------------------+
1 row in set (0.00 sec)
```

### 3. What did you see instead (Required)
results from tidb
```
MySQL [test1]> SELECT STR_TO_DATE('2016_01 Monday', "%X_%V %W");
+-------------------------------------------+
| STR_TO_DATE('2016_01 Monday', "%X_%V %W") |
+-------------------------------------------+
| NULL |
+-------------------------------------------+
1 row in set, 1 warning (0.01 sec)

```

### 4. What is your TiDB version? (Required)
```
MySQL [test1]> select tidb_version();
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version() |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v8.5.1
Edition: Community
Git Commit Hash: fea86c8e35ad4a86a5e1160701f99493c2ee547c
Git Branch: HEAD
UTC Build Time: 2025-01-16 07:38:34
GoVersion: go1.23.4
Race Enabled: false
Check Table Before Drop: false
Store: tikv |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
```