From FLAC: warning: cast between incompatible function types

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### Describe your issue here

Warning during compiling sfml3 on windows 64:
using wingw64 based to use with codeblocks.

Addressing the warning in win_utf8_io.c at line 132:29.

### Your Environment

- OS / distro / window manager: windows 64
- SFML version: 3
- Compiler / toolchain: wingw64
- Special compiler / CMake flags:

### Steps to reproduce

```cpp
#include <SFML/Graphics.hpp>

int main()
{
    sf::RenderWindow window(sf::VideoMode({1280, 720}), "Minimal, complete and verifiable example");
    window.setFramerateLimit(60);

    while (window.isOpen())
    {
        while (const std::optional event = window.pollEvent())
        {
            if (event->is<sf::Event::Closed>())
                window.close();
        }

        window.clear();
        window.display();
    }
}
```

### Expected behavior

Should not give any warnings.

### Actual behavior

Warning during compiling.

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