[doc] php version support update

[Albirew]

In documentation's server configuration, PHP support sops at 8.2
I tried successfully with php8.3 and php8.4, so unless there are known issues i didn't see, i think documentation can be updated.

[nodiscc]

@Albirew hi, yes! The server configuration docs/PHP compatibility docs regularly fall out of date with currently supported versions.

The actual list of supported/tested version is here: https://github.com/shaarli/Shaarli/blob/master/.github/workflows/ci.yml#L9 (may also work with older versions, but they all reached end-of life https://www.php.net/supported-versions.php, so no guarantees.

I will find a way to auto-update the PHP compatibility docs based on the test matrix.

By the way, support for PHP 7.4 and 8.0 was just dropped in d79657a