expire todo count calculations to be consistent with

assigned_open_merge_requests_count and assigned_open_issues_count, which are used in the top header stats.  Also important for a Geo secondary, so that the pending todo stat gets updated on the same frequency as the users open issues/merge requests.

app/models/user.rb

@@ -1054,13 +1054,13 @@ class User < ActiveRecord::Base
   end
 
   def todos_done_count(force: false)
-    Rails.cache.fetch(['users', id, 'todos_done_count'], force: force) do
+    Rails.cache.fetch(['users', id, 'todos_done_count'], force: force, expires_in: 20.minutes) do
       TodosFinder.new(self, state: :done).execute.count
     end
   end
 
   def todos_pending_count(force: false)
-    Rails.cache.fetch(['users', id, 'todos_pending_count'], force: force) do
+    Rails.cache.fetch(['users', id, 'todos_pending_count'], force: force, expires_in: 20.minutes) do
       TodosFinder.new(self, state: :pending).execute.count
     end
   end