pip(deps): update pydoc-markdown requirement from ~=4.3 to ~=4.6

Updates the requirements on [pydoc-markdown](https://github.com/NiklasRosenstein/pydoc-markdown) to permit the latest version.
- [Release notes](https://github.com/NiklasRosenstein/pydoc-markdown/releases)
- [Commits](https://github.com/NiklasRosenstein/pydoc-markdown/commits/v4.6.1)

---
updated-dependencies:
- dependency-name: pydoc-markdown
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements/DEV_REQUIREMENTS.txt

@@ -5,7 +5,7 @@ coverage~=6.1
 isort~=5.10
 moto~=3.0
 pydoc-markdown~=4.3 ; python_version >= '3.7'
-pydoc-markdown~=3.13 ; python_version == '3.6'
+pydoc-markdown~=4.6 ; python_version == '3.6'
 pytest~=7.0
 pytest-cov~=3.0
 pylint~=2.11