WP 6.5: account for new function polyfills

[swissspidy]

WP 6.5 contains a polyfill for array_is_list, which was introduced in PHP 8.1.

Ticket: https://core.trac.wordpress.org/ticket/55105 Commit: https://core.trac.wordpress.org/changeset/57337

[jrfnl]

Thanks @swissspidy ! I've labelled this PR as "wait for upstream" to merge it once WP 6.5 has been released/is close to release.

Note: While the PHP 8.0 functions are not yet flagged by the latest release of PHPCompatibility, they will be once PHPCompatibility 10.0 comes out.

As exclude-ing error codes which don't exist yet does not lead to errors in PHPCS, I'm fine with accepting this PR for the next 2.x release, along the same lines as previously done for PR #35.

[jrfnl]

WP 6.5 has been released in the mean time, so this is good to go.