build(deps): bump ansys-sphinx-theme in /requirements (#435)

Bumps [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme) from 0.16.2 to 0.16.4.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v0.16.2...v0.16.4)

---
updated-dependencies:
- dependency-name: ansys-sphinx-theme
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/requirements_doc.txt

@@ -1,5 +1,5 @@
 Sphinx<8
-ansys-sphinx-theme==0.16.2
+ansys-sphinx-theme==0.16.4
 imageio==2.34.1
 nest-asyncio==1.6.0
 notfound==1.0.2