[clang] [clang][Sema] Ignore the parentheses in the guard of DiagnoseUnexpandedParameterPack (PR #86401)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@dwblaikie Feel free to checkout this patch locally and see if it resolves the original issue - I won't merge it until you confirm it works or discover another issue that goes beyond the scope of this patch. (e.g. another aforementioned issue)

https://github.com/llvm/llvm-project/pull/86401