[Glitch] Ensure tabIndex is number instead of string

Port ec0c104bf2 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/notifications/components/admin_signup.jsx

@@ -78,7 +78,7 @@ export default class NotificationFollow extends ImmutablePureComponent {
     //  Renders.
     return (
       <HotKeys handlers={this.getHandlers()}>
-        <div className={classNames('notification notification-admin-sign-up focusable', { unread })} tabIndex='0'>
+        <div className={classNames('notification notification-admin-sign-up focusable', { unread })} tabIndex={0}>
           <div className='notification__message'>
             <div className='notification__favourite-icon-wrapper'>
               <Icon fixedWidth id='user-plus' />