Fix asset publishing if they were already published (#5734)

Thank you @sebdesign for the fix.

composer.json

@@ -38,7 +38,7 @@
             "@php artisan package:discover --ansi"
         ],
         "post-update-cmd": [
-            "@php artisan vendor:publish --tag=laravel-assets --ansi"
+            "@php artisan vendor:publish --tag=laravel-assets --ansi --force"
         ],
         "post-root-package-install": [
             "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""