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

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eaeltsin wrote:

Okay, this is `E->Final`, which was
- initialized for [VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *E)](https://github.com/llvm/llvm-project/blob/main/clang/lib/Serialization/ASTReaderStmt.cpp#L2233) 
- but missed for [VisitSubstNonTypeTemplateParmPackExpr(SubstNonTypeTemplateParmPackExpr *E)](https://github.com/llvm/llvm-project/blob/main/clang/lib/Serialization/ASTReaderStmt.cpp#L2242)


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