**Describe the unexpected behaviour**

I expect

```sql
select replaceRegexpAll('Hello, World!', '^', 'here: ')
```

to produce 

```
here: Hello, World!
```

in v20, this is the case, and in v21 the result is:

```
here: ello, World!
```

**How to reproduce**

Run the above query in clickhouse v20, then in v21
#pragma once
#include <base/types.h>
#include <Common/Volnitsky.h>
#include <Columns/ColumnString.h>
#include <IO/WriteHelpers.h>
#include "config_functions.h"
#include <Common/config.h>
#if USE_RE2_ST
#    include <re2_st/re2.h>
#else
#    include <re2/re2.h>
#    define re2_st re2
#endif
namespace DB
{
namespace ErrorCodes
{