build(deps): bump ansys-sphinx-theme[autoapi] in /requirements

Bumps [ansys-sphinx-theme[autoapi]](https://github.com/ansys/ansys-sphinx-theme) from 1.5.3 to 1.6.3.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v1.5.3...v1.6.3)

---
updated-dependencies:
- dependency-name: ansys-sphinx-theme[autoapi]
  dependency-version: 1.6.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/requirements_docs.txt

@@ -1,4 +1,4 @@
-ansys-sphinx-theme[autoapi]==1.5.3
+ansys-sphinx-theme[autoapi]==1.6.3
 enum-tools[sphinx]==0.13.0
 graphviz==0.21
 imageio==2.37.0