Ensure tabIndex is number instead of string (#24409)

app/javascript/mastodon/features/direct_timeline/components/conversation.jsx

@@ -144,7 +144,7 @@ class Conversation extends ImmutablePureComponent {
 
     return (
       <HotKeys handlers={handlers}>
-        <div className={classNames('conversation focusable muted', { 'conversation--unread': unread })} tabIndex='0'>
+        <div className={classNames('conversation focusable muted', { 'conversation--unread': unread })} tabIndex={0}>
           <div className='conversation__avatar' onClick={this.handleClick} role='presentation'>
             <AvatarComposite accounts={accounts} size={48} />
           </div>