General: Use static on closures whenever $this is not used to avoid memory leaks.

Props westonruter, jrf, spacedmonkey.
Fixes #58323.


git-svn-id: https://develop.svn.wordpress.org/trunk@55822 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/query/stickies.php

@@ -136,7 +136,7 @@ class Tests_Query_Stickies extends WP_UnitTestCase {
 		$post_ids     = self::factory()->post->create_many( $sticky_count, array( 'post_date' => $post_date ) );
 		add_filter(
 			'pre_option_sticky_posts',
-			function () use ( $post_ids ) {
+			static function () use ( $post_ids ) {
 				return $post_ids;
 			}
 		);