fix: apply correct styles to audio descriptions track menu items (#8770)

## Description
Fix #8769 for mismatched track kind should be plural descriptions
according to definition of `AudioTrackKind`
#8769

## Specific Changes proposed
Corrects `description` to `descriptions`

src/css/components/_audio.scss

@@ -2,15 +2,15 @@
   @extend .vjs-icon-audio;
 }
 
-.video-js .vjs-audio-button + .vjs-menu .vjs-description-menu-item .vjs-menu-item-text .vjs-icon-placeholder,
+.video-js .vjs-audio-button + .vjs-menu .vjs-descriptions-menu-item .vjs-menu-item-text .vjs-icon-placeholder,
 .video-js .vjs-audio-button + .vjs-menu .vjs-main-desc-menu-item .vjs-menu-item-text .vjs-icon-placeholder {
   vertical-align: middle;
   display: inline-block;
   margin-bottom: -0.1em;
 }
 
 // Mark a main-desc-menu-item (main + description) or description item with a trailing Audio Description icon
-.video-js .vjs-audio-button + .vjs-menu .vjs-description-menu-item .vjs-menu-item-text .vjs-icon-placeholder:before,
+.video-js .vjs-audio-button + .vjs-menu .vjs-descriptions-menu-item .vjs-menu-item-text .vjs-icon-placeholder:before,
 .video-js .vjs-audio-button + .vjs-menu .vjs-main-desc-menu-item .vjs-menu-item-text .vjs-icon-placeholder:before {
   font-family: VideoJS;
   content: " \f12e";

src/js/control-bar/audio-track-controls/audio-track-menu-item.js

@@ -51,7 +51,7 @@ class AudioTrackMenuItem extends MenuItem {
     const el = super.createEl(type, props, attrs);
     const parentSpan = el.querySelector('.vjs-menu-item-text');
 
-    if (['main-desc', 'description'].indexOf(this.options_.track.kind) >= 0) {
+    if (['main-desc', 'descriptions'].indexOf(this.options_.track.kind) >= 0) {
       parentSpan.appendChild(Dom.createEl('span', {
         className: 'vjs-icon-placeholder'
       }, {