update: bump the pip-packages group in /docs with 1 update

Updates the requirements on [mkdocs-material](https://github.com/squidfunk/mkdocs-material) to permit the latest version.

Updates `mkdocs-material` to 9.5.6
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.4.14...9.5.6)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-type: direct:production
  dependency-group: pip-packages
...

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

docs/requirements.txt

@@ -1,2 +1,2 @@
-mkdocs-material~=9.4.14
+mkdocs-material~=9.5.6
 mike~=2.0.0