Docs: Clarify that `wp_filter_object_list()` accepts `'not'` as its `$operator` parameter.

Props barryceelen.
See #35225.
Built from https://develop.svn.wordpress.org/trunk@36090


git-svn-id: https://core.svn.wordpress.org/trunk@36055 1a063a9b-81f0-0310-95a4-ce76da25c4cd