[clang] [clang][docs] Fix docs-clang-html. (PR #142387)

[A. Jiang via cfe-commits]

frederick-vs-ja wrote:

I wonder whether it would be better to modify `.github/workflows/docs.yml` together. It seems that modification of some transitively included td files doesn't trigger CI for documentation.

https://github.com/llvm/llvm-project/pull/142387