[12.x] Check if file exists before trying to delete it (#55994)

This avoids the warning "No such file or directory" if the file doesn't exist.

```
$ php artisan config:clear
unlink(/home/jellyfrog/code/librenms/bootstrap/cache/config.php): No such file or directory in /home/jellyfrog/code/librenms/vendor/laravel/framework/src/Illuminate/Filesystem/Filesystem.php on line 308

   INFO  Configuration cache cleared successfully.
```

Author: Jellyfrog

src/Illuminate/Filesystem/Filesystem.php

@@ -305,7 +305,7 @@ public function delete($paths)
 
         foreach ($paths as $path) {
             try {
-                if (@unlink($path)) {
+                if (is_file($path) && @unlink($path)) {
                     clearstatcache(false, $path);
                 } else {
                     $success = false;