Wrong Result in Cast Blob to Json

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```sql
DROP TABLE IF EXISTS t0;
CREATE TABLE t0(c0 BLOB);
INSERT INTO t0 VALUES ('1xx');

SELECT CAST(t0.c0 AS JSON) IS TRUE FROM t0;
```

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

see the following case:

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

```sql
// TiDB
mysql> SELECT CAST(t0.c0 AS JSON) IS TRUE FROM t0;
+-----------------------------+
| CAST(t0.c0 AS JSON) IS TRUE |
+-----------------------------+
| 0 |
+-----------------------------+
1 row in set, 1 warning (0.04 sec)

// MySQL
MySQL [test]> SELECT CAST(t0.c0 AS JSON) IS TRUE FROM t0;
+-----------------------------+
| CAST(t0.c0 AS JSON) IS TRUE |
+-----------------------------+
| 1 |
+-----------------------------+
1 row in set, 1 warning (0.01 sec)
```

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

TiDB v8.5.0