Bump pypandoc from 1.12 to 1.13 in /requirements

Bumps [pypandoc](https://github.com/JessicaTegner/pypandoc) from 1.12 to 1.13.
- [Release notes](https://github.com/JessicaTegner/pypandoc/releases)
- [Changelog](https://github.com/JessicaTegner/pypandoc/blob/master/release.md)
- [Commits](JessicaTegner/pypandoc@v1.12...v1.13)

---
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

@@ -14,7 +14,7 @@ numpydoc==1.6.0
 pandas==2.2.0
 panel==1.3.8
 plotly==5.19.0
-pypandoc==1.12
+pypandoc==1.13
 pytest-sphinx==0.6.0
 pythreejs==2.4.2
 pyvista==0.43.3