fix: add xmlns:thr for in-reply-to refs

lib/pleroma/web/templates/feed/feed/tag.atom.eex

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
 <feed
   xmlns="http://www.w3.org/2005/Atom"
+  xmlns:thr="http://purl.org/syndication/thread/1.0"
   xmlns:activity="http://activitystrea.ms/spec/1.0/"
   xmlns:poco="http://portablecontacts.net/spec/1.0"
   xmlns:ostatus="http://ostatus.org/schema/1.0"

lib/pleroma/web/templates/feed/feed/tag.rss.eex

@@ -1,8 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<rss version="2.0" xmlns:webfeeds="http://webfeeds.org/rss/1.0">
+<rss version="2.0"
+     xmlns:webfeeds="http://webfeeds.org/rss/1.0"
+     xmlns:thr="http://purl.org/syndication/thread/1.0">
   <channel>
 
-
     <title>#<%= @tag %></title>
     <description><%= Gettext.dpgettext("static_pages", "tag feed description", "These are public toots tagged with #%{tag}. You can interact with them if you have an account anywhere in the fediverse.", tag: @tag) %></description>
     <link><%= '#{Routes.tag_feed_url(@conn, :feed, @tag)}.rss' %></link>

lib/pleroma/web/templates/feed/feed/user.atom.eex

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <feed
   xmlns="http://www.w3.org/2005/Atom"
+  xmlns:thr="http://purl.org/syndication/thread/1.0"
   xmlns:activity="http://activitystrea.ms/spec/1.0/"
   xmlns:poco="http://portablecontacts.net/spec/1.0"
   xmlns:ostatus="http://ostatus.org/schema/1.0">

lib/pleroma/web/templates/feed/feed/user.rss.eex

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <rss version="2.0"
      xmlns:atom="http://www.w3.org/2005/Atom"
+     xmlns:thr="http://purl.org/syndication/thread/1.0"
      xmlns:activity="http://activitystrea.ms/spec/1.0/"
      xmlns:ostatus="http://ostatus.org/schema/1.0"
      xmlns:poco="http://portablecontacts.net/spec/1.0">