Bump ansys-sphinx-theme from 0.13.3 to 0.13.4 in /requirements (#380)

Bumps [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme) from 0.13.3 to 0.13.4.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v0.13.3...v0.13.4)

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

Signed-off-by: dependabot[bot] <support@github.com>
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==0.13.3
+ansys-sphinx-theme==0.13.4
 imageio==2.33.1
 nest-asyncio==1.6.0
 notfound==1.0.2