显示一个管理员通知，在核心升级后升级所有站点。

function site_admin_notice() {
	global $wp_db_version, $pagenow;

	if ( ! current_user_can( 'upgrade_network' ) ) {
		return false;
	}

	if ( 'upgrade.php' === $pagenow ) {
		return;
	}

	if ( (int) get_site_option( 'wpmu_upgrade_site' ) !== $wp_db_version ) {
		echo "
" . sprintf(
			/* translators: %s: URL to Upgrade Network screen. */
			__( 'Thank you for Updating! Please visit the Upgrade Network page to update all your sites.' ),
			esc_url( network_admin_url( 'upgrade.php' ) )
		) . '
';
	}
}