ERROR 1105 (HY000): other error: Invalid regexp pattern

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
CREATE TABLE `t0` (
`c` bigint(20) unsigned zerofill NOT NULL,
PRIMARY KEY (`c`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;

SELECT t0.c FROM t0 WHERE ((t0.c)>(((t0.c)REGEXP('{}'))));
```

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

query ok

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

```
ERROR 1105 (HY000): other error: Invalid regexp pattern: Syntax(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
regex parse error:
(?i){}
^
error: repetition operator missing expression
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
)
```

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

```
mysql> select tidb_version();
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version() |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v8.3.0
Edition: Community
Git Commit Hash: 1a0c3ac3292fff7742faa0c00a662ccb66ba40db
Git Branch: HEAD
UTC Build Time: 2024-08-20 10:23:00
GoVersion: go1.21.10
Race Enabled: false
Check Table Before Drop: false
Store: tikv |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
```

Start by running the provided CREATE TABLE and SELECT reproduction against TiDB v8.3.0 and trace the REGEXP expression path. Done means the query succeeds as expected and a regression test covers the '{}' pattern without reporting an invalid regexp pattern.

Written by the indexing model from the issue text.