Resolve "Barrierefreiheit: Blubber Benachrichtigungsstatus ist nicht für Screenreader erkennbar"

Closes #4061

Merge request studip/studip!2907

resources/assets/javascripts/lib/blubber.js

@@ -47,6 +47,7 @@ const Blubber = {
                 subscribe: follow,
             });
         }).then(() => {
+            elements.attr('aria-pressed', follow ? 'true' : 'false');
             elements.toggleClass('unfollowed', !follow);
         }).finally(() => {
             elements.removeClass('loading');

templates/blubber/global_context.php

@@ -7,6 +7,8 @@
        onClick="STUDIP.Blubber.followunfollow('global'); return false;"
        class="followunfollow<?= $unfollowed ? " unfollowed" : "" ?>"
        title="<?= _("Benachrichtigungen für diese Konversation abstellen.") ?>"
+       aria-pressed="<?= $unfollowed ? 'false' : 'true' ?>"
+       role="button"
        data-thread_id="global">
         <?= Icon::create("decline")->asImg(20, ['class' => "follow text-bottom"]) ?>
         <?= Icon::create("notification2")->asImg(20, ['class' => "unfollow text-bottom"]) ?>