Mention pusher/pusher-php-server upgrade from ^4.0|^5.0 to ^5.0 in upgrade guide (#8110)

* docs: mention pusher/pusher-php-server upgrade from ^4.0|^5.0 to ^5.0

See laravel/framework#36528

* Update upgrade.md

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: AlbinoDrought

upgrade.md

@@ -60,7 +60,7 @@ You should update the following dependencies in your application's `composer.jso
 
 </div>
 
-In addition, please replace `facade/ignition` with `"spatie/laravel-ignition": "^1.0"` in your application's `composer.json` file.
+In addition, please replace `facade/ignition` with `"spatie/laravel-ignition": "^1.0"` and `pusher/pusher-php-server` (if applicable) with `"pusher/pusher-php-server": "^5.0"` in your application's `composer.json` file.
 
 Furthermore, the following first-party packages have received new major releases to support Laravel 9.x. If applicable, you should read their individual upgrade guides before upgrading: