MAINT: Bump the doc-deps group across 1 directory with 2 updates

Updates the requirements on [ansys-sphinx-theme](https://github.com/ansys/ansys-sphinx-theme) and [snowballstemmer](https://github.com/snowballstem/snowball) to permit the latest version.

Updates `ansys-sphinx-theme` from 1.3.3 to 1.6.3
- [Release notes](https://github.com/ansys/ansys-sphinx-theme/releases)
- [Commits](ansys/ansys-sphinx-theme@v1.3.3...v1.6.3)

Updates `snowballstemmer` to 3.0.1
- [Changelog](https://github.com/snowballstem/snowball/blob/master/NEWS)
- [Commits](snowballstem/snowball@v2.0.0...v3.0.1)

---
updated-dependencies:
- dependency-name: ansys-sphinx-theme
  dependency-version: 1.6.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: doc-deps
- dependency-name: snowballstemmer
  dependency-version: 3.0.1
  dependency-type: direct:production
  dependency-group: doc-deps
...

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

Author: dependabot[bot]

doc/requirements.txt

@@ -1,7 +1,7 @@
-ansys-sphinx-theme==1.3.3
+ansys-sphinx-theme==1.6.3
 Sphinx==8.2.3
 sphinx-copybutton==0.5.2
 sphinx-design==0.6.1
 sphinx-notfound-page==1.1.0
 sphinxemoji==0.3.1
-snowballstemmer<3
+snowballstemmer<4