[clang] [Clang] Fix dependency computation for pack indexing expression (PR #91933)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 approved this pull request.

Thanks for the prompt fix! I think this looks good now, but please wait for @erichkeane for the final stamp.

https://github.com/llvm/llvm-project/pull/91933