Geo: address review comments

app/services/geo/base_sync_service.rb

+require 'securerandom'
+
 module Geo
   # The clone_url_prefix is used to build URLs for the Geo synchronization
   # If this is missing from the primary node we raise this exception
@@ -173,7 +175,7 @@ module Geo
 
     def disk_path_temp
       unless @disk_path_temp
-        random_string = (0...6).map { ('a'..'z').to_a.sample }.join
+        random_string = SecureRandom.hex(7)
         @disk_path_temp = "#{repository.disk_path}_#{random_string}"
       end
 

app/services/geo/repository_sync_service.rb

@@ -34,6 +34,7 @@ module Geo
       log_error('Error syncing repository', e)
     rescue Gitlab::Git::Repository::NoRepository => e
       log_error('Invalid repository', e)
+      log_info('Setting force_to_redownload flag')
       registry.update(force_to_redownload_repository: true)
       log_info('Expiring caches')
       project.repository.after_create