MAINT: bump ansys-sphinx-theme in /doc in the doc-deps group

Bumps the doc-deps group in /doc with 1 update: [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme).


Updates `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
  dependency-group: doc-deps
...

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

doc/requirements.txt

@@ -1,4 +1,4 @@
-ansys-sphinx-theme==0.15.0
+ansys-sphinx-theme==0.15.1
 Sphinx==7.2.6
 sphinx-copybutton==0.5.2
 sphinx-design==0.5.0