[clang] [clang] Substitute alias templates from correct context (PR #75069)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

@rupprecht , no, this is not expected. Please feel free to revert since it is night in my time zone. Otherwise I will revert tomorrow.

https://github.com/llvm/llvm-project/pull/75069