deps(pip): bump the pip group in /docs with 1 update (#410)

Bumps the pip group in /docs with 1 update: [mkdocs-material](https://github.com/squidfunk/mkdocs-material).


Updates `mkdocs-material` from 9.5.4 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@9.5.4...9.5.6)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: pip
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/requirements.txt

@@ -1 +1 @@
-mkdocs-material==9.5.4
+mkdocs-material==9.5.6