build: bump ansys-sphinx-theme from 1.6.1 to 1.6.3 in the doc group

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


Updates `ansys-sphinx-theme` from 1.6.1 to 1.6.3
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v1.6.1...v1.6.3)

---
updated-dependencies:
- dependency-name: ansys-sphinx-theme
  dependency-version: 1.6.3
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: doc
...

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

Author: dependabot[bot]

pyproject.toml

@@ -98,7 +98,7 @@ tests = [
     "pytest-mpl==0.17.0",
 ]
 doc = [
-    "ansys-sphinx-theme==1.6.1",
+    "ansys-sphinx-theme==1.6.3",
     "build==1.3.0",
     "jupyterlab==4.4.9",
     "jupytext==1.17.3",