ManagedFile element wrong #accept assignment

Problem/Motivation

ManagedFile element has wrong #accept assignment

$element['upload']['#attributes'] = ['accept' => $element['#accept']];

It removes previously set attributes.

Steps to reproduce

    if (!empty($element['#description'])) {
      $element['upload']['#attributes']['aria-describedby'] = $element['#id'] . '--description';
    }

    if (!empty($element['#accept'])) {
      $element['upload']['#attributes'] = ['accept' => $element['#accept']];
    }