Fix YouTube subscription import parser

src/invidious.cr

@@ -1492,9 +1492,10 @@ post "/data_control" do |env|
           end
         end
       when "import_youtube"
-        subscriptions = XML.parse(body)
-        user.subscriptions += subscriptions.xpath_nodes(%q(//outline[@type="rss"])).map do |channel|
-          channel["xmlUrl"].match(/UC[a-zA-Z0-9_-]{22}/).not_nil![0]
+        subscriptions = JSON.parse(body)
+
+        user.subscriptions += subscriptions.as_a.compact_map do |entry|
+          entry["snippet"]["resourceId"]["channelId"].as_s
         end
         user.subscriptions.uniq!