php 8.4: ini_set(): session.sid_length INI setting is deprecated

I was trying to use CI3 with PHP8.4.
I'm facing this error:

```
An uncaught Exception was encountered

Type: ErrorException

Message: ini_set(): session.sid_length INI setting is deprecated

Filename: .../vendor/codeigniter/framework/system/libraries/Session/Session.php

Line Number: 426
```

https://github.com/codeigniter4/CodeIgniter4/pull/9139 might be of interest.