Add test redirect for changeable link

Author: yasulab

config/routes.rb

@@ -31,6 +31,7 @@
   get "/docs/_calendar-kirie",    to: redirect('/calendar/kirie')
   get "/docs/_thanks",            to: redirect('/thanks')
 
+  get "/redirects/202407",        to: redirect('https://www.facebook.com/groups/coderdojo.jp.champions')
   get "/youtube",                 to: redirect('https://www.youtube.com/CoderDojoJapan')
   get "/brand",                   to: redirect('/docs/brand-guidelines')
   get "/calendar",                to: redirect('/calendar/yohei')