[clang] [Clang][Sema] Fix templated array size calculation. (PR #96464)

[via cfe-commits]

awson wrote:

> If you have approvals you don't have to wait for other reviewers unless they have made a comment that required a change and you them to confirm the fix or they explicitly blocked the review.

I believe I have no write access to the repo.

Could you, please, merge this?

@cor3ntin, @erichkeane, @AaronBallman ?

https://github.com/llvm/llvm-project/pull/96464