Don't modify original config object

Use `Marshal` to avoid mutating the original copy of the storage config.

files/gitlab-cookbooks/gitaly/libraries/gitaly.rb

@@ -163,7 +163,8 @@ module Gitaly
 
     # Validate that no storages are sharing the same path.
     def check_duplicate_storage_paths
-      storages = Gitlab['gitaly']['configuration']['storage'].dup
+      # Deep copy storages to avoid mutating the original.
+      storages = Marshal.load(Marshal.dump(Gitlab['gitaly']['configuration']['storage']))
 
       storages.each do |storage|
         storage[:realpath] =