Docs: Add private access notation to the DocBlock for the core `_wp_handle_upload()` function.

See #32246.


git-svn-id: https://develop.svn.wordpress.org/trunk@36473 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/file.php

@@ -224,6 +224,7 @@ function validate_file_to_edit( $file, $allowed_files = '' ) {
  * Handle PHP uploads in WordPress, sanitizing file names, checking extensions for mime type,
  * and moving the file to the appropriate directory within the uploads directory.
  *
+ * @access private
  * @since 4.0.0
  *
  * @see wp_handle_upload_error