[clang] [Clang][Sema] Fix crash in containsUnexpandedParameterPacks (PR #182484)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@Ayush3941 please don't silently change the description of a PR, I was just confused by this as the change in description made me think I had missed the correct diagnostic.

Also, can you please indicate if an LLM was used for this PR?

https://github.com/llvm/llvm-project/pull/182484