Move internal knowledge about expiring caches to the Repository class

app/models/repository.rb

@@ -426,6 +426,13 @@ class Repository
     expire_branches_cache
   end
 
+  # Runs code after a repository has been synced.
+  def after_sync
+    expire_all_method_caches
+    expire_branch_cache
+    expire_content_cache
+  end
+
   # Runs code after a new commit has been pushed.
   def after_push_commit(branch_name)
     expire_statistics_caches

app/services/geo/repository_backfill_service.rb

@@ -52,9 +52,7 @@ module Geo
         end
 
         log('Expiring caches')
-        project.repository.expire_all_method_caches
-        project.repository.expire_branch_cache
-        project.repository.expire_content_cache
+        project.after_sync
 
         finished_at = DateTime.now
       rescue Gitlab::Shell::Error => e