[Glitch] Add at-symbol prepended to mention span title

Port 7731fbbba7 to glitch-soc

Co-authored-by: Sam BC <samuel.balbirnie-cumming@xdesign.com>
Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/components/status_content.jsx

@@ -163,7 +163,7 @@ class StatusContent extends PureComponent {
 
       if (mention) {
         link.addEventListener('click', this.onMentionClick.bind(this, mention), false);
-        link.setAttribute('title', mention.get('acct'));
+        link.setAttribute('title', `@${mention.get('acct')}`);
         if (rewriteMentions !== 'no') {
           while (link.firstChild) link.removeChild(link.firstChild);
           link.appendChild(document.createTextNode('@'));