When saving options from the Settings page, include the `'ping_sites'` option in the allowed "writing" options list only when the `'blog_public'` option is `'1'`.
Fixes a PHP 8.1 and above "null to non-nullable" deprecation notice in `sanitize_option()` ([https://core.trac.wordpress.org/browser/trunk/src/wp-includes/formatting.php?annotate=blame#L4952 which happens when here] as part of [22255]):
{{{
Deprecated: explode(): Passing null to parameter #2 ($string) of type string is deprecated in .../wp-includes/formatting.php
}}}
**Explanation**
[https://developer.wordpress.org/apis/options/#writing Per the documentation], the `ping_sites` option requires the `'blog_public'` option to have a value of `'1'` and must be a `string` data type. `null` is not valid for this option.
The relationship between the 2 options shows itself in the `options-writing.php` code ([https://core.trac.wordpress.org/browser/tags/6.5.4/src/wp-admin/options-writing.php#L233 shown here] and in [4326]), as the `textarea#ping_sites` only renders when `'1' === get_option( 'blog_public' )`.
**What happens if `'blog_public'` is not `'1'`?**
The `'ping_sites'` option will not be a field on the page. Upon saving:
* HTTP POST (`$_POST`) does not include `'ping_sites'`.
* Before this commit:
* The [https://core.trac.wordpress.org/browser/trunk/src/wp-admin/options.php#L333 option's value was set to] `null` before being passed to `update_option()`.
* `update_option()` invokes `sanitize_option()`.
* A `null` value for the `'ping_sites'` case was passed to `explode()`, which threw a deprecation notice on PHP 8.1 and above.
* With this commit, the `'ping_sites'` option is no longer included in the allow list and thus will not be passed to `update_options()` > `sanitize_option()` > `explode()`.
Follow-up to [22255], [12825], [4326], [949].
Props kitchin, SergeyBiryukov, swissspidy, devmuhib, rajinsharwar, hellofromTonya.
Fixes#59818.
Built from https://develop.svn.wordpress.org/trunk@58425
git-svn-id: http://core.svn.wordpress.org/trunk@57874 1a063a9b-81f0-0310-95a4-ce76da25c4cd