Fix NotificationMailer failing when receiving mention with media from remote instance (#11765)

Author: mayaeh

app/views/notification_mailer/_status.html.haml

@@ -36,7 +36,10 @@
                                 - if status.media_attachments.size > 0
                                   %p
                                     - status.media_attachments.each do |a|
-                                      = link_to medium_url(a), medium_url(a)
+                                      - if status.local?
+                                        = link_to medium_url(a), medium_url(a)
+                                      - else
+                                        = link_to a.remote_url, a.remote_url
 
                               %p.status-footer
                                 = link_to l(status.created_at), web_url("statuses/#{status.id}")