`REGEXP_LIKE` shouldn't accept arguments with mixed collation

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

Run the SQL `SELECT REGEXP_LIKE(BINARY 'ABC', 'abc', 'i');`

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

```
mysql> SELECT REGEXP_LIKE(BINARY 'ABC', 'abc', 'i');
ERROR 3995 (HY000): Character set 'binary' cannot be used in conjunction with 'utf8mb4_bin' in call to regexp_like.
```

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

```
mysql> SELECT REGEXP_LIKE(BINARY 'ABC', 'abc', 'i');
+---------------------------------------+
| REGEXP_LIKE(BINARY 'ABC', 'abc', 'i') |
+---------------------------------------+
| 1 |
+---------------------------------------+
1 row in set (0.00 sec)
```

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