[6.x] Better docblocks for Event::listen

[imanghafoori1]

This makes sense since the 'setupWildcardListen' method is documented like this.
Which we directly forward the $listener to it.

/**
 * Setup a wildcard listener callback.
 *
 * @param  string  $event
 * @param  \Closure|string  $listener
 * @return void
 */
protected function setupWildcardListen($event, $listener)
{
    $this->wildcards[$event][] = $this->makeListener($listener, true);

    $this->wildcardsCache = [];
}