Docs: Add documentation for the `wp_maybe_auto_update` action.

Props MikeGillihan.
Fixes #43301.


Built from https://develop.svn.wordpress.org/trunk@44609


git-svn-id: http://core.svn.wordpress.org/trunk@44440 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/update.php

@@ -232,6 +232,11 @@ function wp_version_check( $extra_stats = array(), $force_check = false ) {
 
 	// Trigger background updates if running non-interactively, and we weren't called from the update handler.
 	if ( $doing_cron && ! doing_action( 'wp_maybe_auto_update' ) ) {
+		/**
+		 * Fires during wp_cron, starting the auto update process.
+		 *
+		 * @since 3.9.0
+		 */
 		do_action( 'wp_maybe_auto_update' );
 	}
 }

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-beta1-44608';
+$wp_version = '5.1-beta1-44609';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.