Bump sphinx from 7.1.2 to 7.2.6 in /requirements

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.1.2 to 7.2.6.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.1.2...v7.2.6)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements/requirements_doc.txt

@@ -9,7 +9,7 @@ pyvista==0.40.4
 vtk==9.2.6
 
 # Documentation dependencies
-Sphinx==7.1.2
+Sphinx==7.2.6
 numpydoc==1.5.0
 ansys-sphinx-theme==0.10.3
 sphinx-copybutton==0.5.2