Bump pypandoc from 1.11 to 1.12 in /requirements

Bumps [pypandoc](https://github.com/JessicaTegner/pypandoc) from 1.11 to 1.12.
- [Release notes](https://github.com/JessicaTegner/pypandoc/releases)
- [Changelog](https://github.com/JessicaTegner/pypandoc/blob/master/release.md)
- [Commits](JessicaTegner/pypandoc@v1.11...v1.12)

---
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

@@ -21,4 +21,4 @@ sphinx-autobuild==2021.3.14
 sphinx-autodoc-typehints==1.24.0
 sphinx-notfound-page==1.0.0
 panel==1.2.1
-pypandoc==1.11
+pypandoc==1.12