build: bump ansys-sphinx-theme[autoapi] from 1.2.4 to 1.3.1 in /requirements (#2058)

Bumps [ansys-sphinx-theme[autoapi]](https://github.com/ansys/ansys-sphinx-theme) from 1.2.4 to 1.3.1.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v1.2.4...v1.3.1)

---
updated-dependencies:
- dependency-name: ansys-sphinx-theme[autoapi]
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/requirements_docs.txt

@@ -1,4 +1,4 @@
-ansys-sphinx-theme[autoapi]==1.2.4
+ansys-sphinx-theme[autoapi]==1.3.1
 enum-tools[sphinx]==0.12.0
 graphviz==0.20.1
 imageio==2.36.0