[clang] [Clang] Fix finding instantiated decls for class template specializations during instantiation (PR #72346)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Thanks for the review, @erichkeane. I am wondering what you mean by this needs "release note"?

Ah, yes!  See `docs/ReleaseNotes.rst`.  For each new bug fix (and most patches!) we require an entry into our release notes document.

https://github.com/llvm/llvm-project/pull/72346