[clang] [clang] Add release note for int->enum conversion change. (PR #144407)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I see you've done this :)  (Sorry, going through my WG21 backlog!).  It would be neat if we mentioned how to FIX the boost issue/elaborated a bit on summarizing the discussion), but this is fine-as is.

https://github.com/llvm/llvm-project/pull/144407