Update gitlab-mail_room to v0.0.23

What does this MR do?

This only has minor fixes but allows for the v2 of oauth2 gem and gets rid of an unnecessary io-wait gem dependency, which will need to be updated for Ruby 3.1+. The io-wait version was pinned due to #6471 (closed), which has now been resolved upstream (https://github.com/ruby/io-wait/commit/1060f9348c60a62e4a5e00e718a605cef00f7bbd).

Diff: https://my.diffend.io/gems/gitlab-mail_room/0.0.20/0.0.23

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened: gitlab-org/build/CNG!1335 (merged)