PHP 8.1

After update ci to 4.15 and update php 8.1 i has some error

I must change one function

```
system/Database/BaseConnection.php
/**
* Returns the number of seconds with microseconds that it took
* to connect to the database.
*
* Used by the Debug Toolbar's timeline.
*/
public function getConnectDuration(int $decimals = 6): string
{
return number_format(intval($this->connectDuration), $decimals);
}
```