Fix renaming files with custom model

Fixes renaming of files when using a custom model with a primary key name other than 'id'.

src/MediaCollections/Filesystem.php

@@ -298,7 +298,7 @@ protected function renameMediaFile(Media $media): void
 
     protected function renameConversionFiles(Media $media): void
     {
-        $mediaWithOldFileName = config('media-library.media_model')::find($media->id);
+        $mediaWithOldFileName = config('media-library.media_model')::find($media->getKey());
         $mediaWithOldFileName->file_name = $mediaWithOldFileName->getOriginal('file_name');
 
         $conversionDirectory = $this->getConversionDirectory($media);