[clang] [clang][Sema] Avoid non-empty unexpanded pack assertion for FunctionParmPackExpr (PR #69224)

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cor3ntin wrote:

> Instead of putting it inside an assertion, how about adding a check for FunctionParmPackExpr separately? I mean,

If that works it would be fine with me, yes

https://github.com/llvm/llvm-project/pull/69224