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_docs.txt

@@ -4,7 +4,7 @@ graphviz==0.20.1
 imageio==2.36.0
 imageio-ffmpeg==0.5.1
 nbsphinx==0.9.5
-pypandoc==1.14
+pypandoc==1.15
 pytest-sphinx==0.6.3
 pyvista==0.44.2
 sphinx==7.4.7