[clang] [clang] fix serialization of SubstNonTypeTemplateParmExpr (PR #134560)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

Yeah I see, so this was actually missed previously in another node, `SubstNonTypeTemplateParmPackExpr`, which during substitution propagates this flag to `SubstNonTypeTemplateParmExpr`.

https://github.com/llvm/llvm-project/pull/134560