Issue #3437752 by lhridley: Fix FileUploadResource::$fileSystem documented...

Issue #3437752 by lhridley: Fix FileUploadResource::$fileSystem documented type to match the constructor typehint

core/modules/file/src/Plugin/rest/resource/FileUploadResource.php

@@ -92,7 +92,7 @@ class FileUploadResource extends ResourceBase {
   /**
    * The file system service.
    *
-   * @var \Drupal\Core\File\FileSystem
+   * @var \Drupal\Core\File\FileSystemInterface
    */
   protected $fileSystem;