Add content-type to status source in glitch-soc

app/serializers/rest/status_source_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class REST::StatusSourceSerializer < ActiveModel::Serializer
-  attributes :id, :text, :spoiler_text
+  attributes :id, :text, :spoiler_text, :content_type
 
   def id
     object.id.to_s