Fix setcookie() documentation for invalid options in PHP 8.0+

[lacatoire]

The setcookie() documentation states that passing an invalid key in the options array triggers an E_WARNING.

Since PHP 8.0, invalid option keys throw a ValueError instead. This PR updates the documentation to accurately reflect the current behavior while preserving the pre-8.0 behavior for reference.

Issue: #4985

[Girgias]

Thanks for working on the doc! Please amend following the comments. :)

[lacatoire]

Thanks for the review @Girgias
I’ve updated the PR accordingly: the error behavior has been moved to a dedicated errors section, the corresponding changelog entry was added, and the sections have been reordered to match the required structure.