Docs: Correct `@since` tag for `do_mu_upgrade` hook, for consistency with `after_mu_upgrade` and `wpmu_upgrade_site`.

See #47110.
Built from https://develop.svn.wordpress.org/trunk@45642


git-svn-id: http://core.svn.wordpress.org/trunk@45453 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/admin.php

@@ -60,7 +60,7 @@ if ( get_option( 'db_upgraded' ) ) {
 		 * If the network is 50 sites or less, it will run every time. Otherwise,
 		 * it will throttle itself to reduce load.
 		 *
-		 * @since 3.0.0
+		 * @since MU (3.0.0)
 		 *
 		 * @param bool $do_mu_upgrade Whether to perform the Multisite upgrade routine. Default true.
 		 */

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45641';
+$wp_version = '5.3-alpha-45642';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.