Bump ansys-sphinx-theme from 0.5.1 to 0.5.2 in /requirements (#461)

Bumps [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme) from 0.5.1 to 0.5.2.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v0.5.1...v0.5.2)

---
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>

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

requirements/requirements_docs.txt

@@ -1,6 +1,6 @@
 pypandoc==1.8.1
 pyvista==0.36.1
-ansys_sphinx_theme==0.5.1
+ansys_sphinx_theme==0.5.2
 nbsphinx==0.8.9
 pytest-sphinx==0.5.0
 sphinx-autobuild==2021.3.14