Bump ansys-sphinx-theme from 0.16.5 to 0.16.6 in /requirements

Bumps [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme) from 0.16.5 to 0.16.6.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v0.16.5...v0.16.6)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements/requirements_doc.txt

@@ -2,7 +2,7 @@
 ansys-mechanical-core==0.11.1
 
 # Documentation dependencies
-ansys-sphinx-theme==0.16.5
+ansys-sphinx-theme==0.16.6
 grpcio==1.64.1
 imageio==2.34.1
 imageio-ffmpeg==0.5.1