[clang] [Clang][Sema] Fix type of enumerators in incomplete enumerations (PR #84068)

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Sirraide wrote:

> > Also, this probably needs a release note.
> 
> If you want I'll add one but this bug has been on main no longer than a week, so I didnt think it would be necessary.

I see. Yeah, I don’t think we really need one if the bug was introduced and fixed in the same version.

https://github.com/llvm/llvm-project/pull/84068