[clang] [Clang][Sema] Differentiate between partial/explicit specializations when diagnosing unexpanded packs (PR #72015)

[Krystian Stasiowski via cfe-commits]

sdkrystian wrote:

@erichkeane Unless you would like someone else to review this, could you please merge this when you have time? I don't have write access 🙂

https://github.com/llvm/llvm-project/pull/72015