[12.x] Fix: getApplication() return type

[alipowerful7]

    /**
     * The application instance.
     *
     * @var \Illuminate\Contracts\Container\Container
     */
    protected $app;

Wrong return:

    /**
     * Get the application instance used by the manager.
     *
     * @return \Illuminate\Contracts\Foundation\Application
     */
    public function getApplication()
    {
        return $this->app;
    }

Correct return:

    /**
     * Get the application instance used by the manager.
     *
     * @return \Illuminate\Contracts\Container\Container
     */
    public function getApplication()
    {
        return $this->app;
    }