[clang] [clang][Sema] Fix a CTAD regression after 42239d2e9 (PR #86914)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

(Since there haven't been any changes besides comments after the very first commit, which has passed the CI, so I'm landing it anyway.)

https://github.com/llvm/llvm-project/pull/86914