[clang] [Clang] accept @tparam on variable template partial specializations (PR #147219)

[Aaron Ballman via cfe-commits]

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

LGTM, with a small nit. (Feel free to land once addressed, additional review not required.)

https://github.com/llvm/llvm-project/pull/147219