[clang] [Clang][Sema] Fix Wswitch-default bad warning in template (PR #76007)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

Can you add more details to you summary "https://github.com/llvm/llvm-project/pull/73077 added -Wswitch-default diagnostic but it produced false positives in templates. This PR will address that issue" 


https://github.com/llvm/llvm-project/pull/76007