Beta Update Icon API returns invalid mime type error for valid image files.

[wcarson]

Trying to use Beta.IconsAPI.SetIcon to update an application icon. The method returns an HTTP 400 error with the following body, even when the image file is a valid image (image/png):

{
  "detailCode": "400",
  "trackingId": "369bd3e94d364b62a5ff2b2dcebed5c5",
  "messages": [
    {
      "locale": "en",
      "localeOrigin": "DEFAULT",
      "text": "Image must be one of the following formats: image/png, image/jpeg."
    }
  ]
}

The image file being used can successfully be uploaded using this API via Postman (or Go using standard http library)