[clang] Fix assertion failure during conversion function overload resolution. (PR #98671)

[Daniel M. Katz via cfe-commits]

katzdm wrote:

> > > LGTM, but please add a release note so users know about the fix.
> > 
> > 
> > @AaronBallman Appreciate the reminder! Done.
> 
> Thanks! Do you need someone to land the changes?

Yep, I don't have commit privilege - would appreciate the help :)

https://github.com/llvm/llvm-project/pull/98671