build: Bump ansys-sphinx-theme from 0.15.0 to 0.15.1 in /requirements

Bumps [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme) from 0.15.0 to 0.15.1.
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v0.15.0...v0.15.1)

---
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

@@ -1,4 +1,4 @@
-ansys-sphinx-theme==0.15.0
+ansys-sphinx-theme==0.15.1
 pyyaml==6.0.1
 Sphinx==7.2.6
 sphinx-copybutton==0.5.2