build(deps): bump pypandoc from 1.14 to 1.15 in /requirements

Bumps [pypandoc](https://github.com/JessicaTegner/pypandoc) from 1.14 to 1.15.
- [Release notes](https://github.com/JessicaTegner/pypandoc/releases)
- [Changelog](https://github.com/JessicaTegner/pypandoc/blob/master/release.md)
- [Commits](JessicaTegner/pypandoc@v1.14...v1.15)

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

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

requirements/requirements_doc.txt

@@ -3,7 +3,7 @@ ansys-sphinx-theme==1.2.6
 imageio==2.36.1
 nest-asyncio==1.6.0
 notfound==1.0.2
-pypandoc==1.14
+pypandoc==1.15
 pyvista==0.43.9
 sphinx-copybutton==0.5.2
 sphinx-gallery==0.18.0