Increase reindexing threshold to 10 days

This excludes indexes that have been worked on e.g. the preceding
weekend.

Relates to
https://gitlab.com/gitlab-com/gl-infra/production/-/issues/5069#note_618889225

lib/gitlab/database/reindexing/reindex_action.rb

@@ -10,7 +10,7 @@ module Gitlab
         enum state: { started: 0, finished: 1, failed: 2 }
 
         # Amount of time to consider a previous reindexing *recent*
-        RECENT_THRESHOLD = 7.days
+        RECENT_THRESHOLD = 10.days
 
         scope :recent, -> { where(state: :finished).where('action_end > ?', Time.zone.now - RECENT_THRESHOLD) }