[clang-tools-extra] [clang-doc] Fix `</section>` mismatch in the namespace template (PR #168966)

[Erick Velez via cfe-commits]

evelez7 wrote:

### Merge activity

* **Nov 21, 7:30 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.com/github/pr/llvm/llvm-project/168966).


https://github.com/llvm/llvm-project/pull/168966