auto-gen-config command fails with Configuration file not found

[nobuyo]

The auto-gen-config command fails if an optional config in a subdirectory is given as an option.

---

Expected behavior

The command should finish successfully.

Actual behavior

The command fails with following error:

$ [bundle exec] rubocop --auto-gen-config --config test/.rubocop_wip.yml
Configuration file not found: /Users/nobuyo/dev/rubocop-custom-config-regenerate-todo-demo/test/.rubocop_todo.yml

Steps to reproduce the problem

1. Create an offensive ruby file, and ./dir/.rubocop_config.yml.
2. Run rubocop --auto-gen-config --config dir/.rubocop_config.yml.
3. Run rubocop --config dir/.rubocop_config.yml.

RuboCop version

$ [bundle exec] rubocop -V
1.29.1 (using Parser 3.1.2.0, rubocop-ast 1.18.0, running on ruby 3.1.2 x86_64-darwin21)