[clang] [clang][Sema] Fix assertion in `tryDiagnoseOverloadedCast` (PR #108021)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Thank you for the fix.

Is this from a bug report, if so it should be mentioned in the summary.

The summary itself could be a big clearer, maybe a small code example could help.

I think this also needs a release note.

https://github.com/llvm/llvm-project/pull/108021