Get access to ref on Transition.Child

[arkrosclou]

As a continuation of this issue #273
ref still doesn't work when used on <Transition.Child>
tested on @headlessui/react@^1.6.1 and @headlessui/react@insiders versions

code: https://github.com/ARkrOSClou/headlessui_ref_issue/blob/main/src/App.js
build: https://headlessui-ref-issue.vercel.app/