[clang] [Clang] Fix false-positive fallthrough warning (#230802) (PR #234848)

[Adinesh Reddy via cfe-commits]

Adinesh-Reddy wrote:

> Please add a release note entry to `clang/docs/ReleaseNotes.md` so that users can know the improvement.

i update,can you check it 

https://github.com/llvm/llvm-project/pull/234848