[clang] [Sema] Fix assertion error in Sema::FindInstantiatedDecl (PR #96509)

[Alejandro Álvarez Ayllón via cfe-commits]

alejandro-alvarez-sonarsource wrote:

> Thanks for the fix; I think this makes sense. Can you provide a release note?

Added (and fixed the conflict)

https://github.com/llvm/llvm-project/pull/96509