Fix: Add guards to backup to exit early on deleted accounts (#40053)

app/workers/backup_worker.rb

@@ -17,8 +17,10 @@ class BackupWorker
   end
 
   def perform(backup_id)
-    backup = Backup.find(backup_id)
-    user   = backup.user
+    backup = Backup.find_by(id: backup_id)
+    return true if backup&.user.nil?
+
+    user = backup.user
 
     BackupService.new.call(backup)