[clang-tools-extra] [clang-doc] Add Mustache HTML output to namespace test (PR #169107)

[Erick Velez via cfe-commits]

evelez7 wrote:

### Merge activity

* **Nov 24, 6:07 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.com/github/pr/llvm/llvm-project/169107).


https://github.com/llvm/llvm-project/pull/169107