Merge branch 'rs-require-backup-files' into 'master'

Explicitly require backup/files

Fixes a test failure we were seeing on CI after merging !1520

See merge request !1731

lib/backup/builds.rb

+require 'backup/files'
+
 module Backup
   class Builds < Files
     def initialize

lib/backup/uploads.rb

+require 'backup/files'
+
 module Backup
   class Uploads < Files