Set const_get to not inherit scope

Fix the one constant passed into BackgroundMigration which was fully
qualified.

lib/gitlab/background_migration.rb

@@ -77,11 +77,9 @@ module Gitlab
       enqueued_job?([retry_set], migration_class)
     end
 
-    # rubocop:disable Cop/ConstGetInheritFalse
     def self.migration_class_for(class_name)
-      const_get(class_name)
+      const_get(class_name, false)
     end
-    # rubocop:enable Cop/ConstGetInheritFalse
 
     def self.enqueued_job?(queues, migration_class)
       queues.each do |queue|

lib/gitlab/background_migration/backfill_project_fullpath_in_repo_config.rb

@@ -171,7 +171,11 @@ module Gitlab
         end
 
         def schedule_retry(project, retry_count)
-          BackgroundMigrationWorker.perform_in(RETRY_DELAY, self.class::RetryOne.name, [project.id, retry_count])
+          # Constants provided to BackgroundMigrationWorker must be within the
+          # scope of Gitlab::BackgroundMigration
+          retry_class_name = self.class::RetryOne.name.sub('Gitlab::BackgroundMigration::', '')
+
+          BackgroundMigrationWorker.perform_in(RETRY_DELAY, retry_class_name, [project.id, retry_count])
         end
       end