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

[Alejandro Álvarez Ayllón via cfe-commits]

alejandro-alvarez-sonarsource wrote:

Thanks! Do you mind merging the PR? I do not have permission to do so.

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