title: VoiceOver won't announce NSAccessibility Notification
body: <p>I'm working to add accessibility to a custom UI element in an existing macOS codebase. We've got a custom error window that appears when an error occurs, and I'm trying to get VoiceOver to announce the error when it occurs.</p>
  
  <p>Currently, I'm trying to use the <a href="https://developer.apple.com/documentation/appkit/nsaccessibility/1534572-post" rel="nofollow noreferrer"><code>NSAccessibility.post(element: Any, notification: NSAccessibility.Notification, userInfo: [NSAccessibility.NotificationUserInfoKey : Any]?)</code></a> method, but while the code is run, the notification is not spoken.</p>
  
  <p>Here's what I've currently got in my NSViewController:</p>
  
  <pre class="lang-swift prettyprint-override"><code>NSAccessibility.post(element: self, notification: .announcementRequested, userInfo: [
      .announcement: NSLocalizedString("CANT_CONNECT_ERROR", comment: "Error string for connection failure"),
      .priority: NSAccessibilityPriorityLevel.high
  ])
  </code></pre>
  
  <p>My expectation was that, using the <code>.announcementRequested</code> option, VoiceOver should automatically pick this up and speak the announcement, but no luck. I've tried using different notification types, tried putting in a hardcoded string value in the <code>.announcement</code> argument, and tried using <code>.rawValue</code> and <code>90</code> for the <code>.priority</code> argument.</p>