Content Type Header No Longer Being Attached

Problem/Motivation

All the PDF files are now opening as normal text rather then as a PDF. After researching, I believe it's connected with the most recent update to symphony (6.1.5). From this issue they are no longer attaching the mime type based on the file but now based on the request. I am not entirely sure how to change the request but as a simple fix we can attach the correct Content-Type header before sending over.

Proposed resolution

By adding this code at the end of the controller, it will always grab the correct mime type.

if (!$response->headers->has('Content-Type')) {
      $response->headers->set('Content-Type', $file->getMimeType() ?: 'application/octet-stream');
    }