Avoid duplicate notifications

This should really be a property of the conference, will have to clean
up later.

app/subscribers/telegram_bot_subscriber.rb

@@ -16,6 +16,8 @@ class TelegramBotSubscriber
     session = event.payload[:record]
     changes = event.payload[:changes]
 
+    return if session.conference.slug.ends_with?("-more")
+
     return unless changes.any? do |attr, (from, to)|
       %w[title language status starts_at ends_at stage_id].include? attr
     end
@@ -39,6 +41,8 @@ class TelegramBotSubscriber
     session_speaker = event.payload[:record]
     session = session_speaker.session
 
+    return if session.conference.slug.ends_with?("-more")
+
     return unless session.conference.relevant_stages.include? session.stage
 
     message = "<b><a href=\"#{conference_session_url(session.conference, session, host: 'rescheduled.c3lingo.org', protocol: 'https')}\">Session #{session.title}</a></b>\n<b>Speaker Change</b>\n" +