build(deps): bump mkdocs-material from 9.5.3 to 9.5.6 in /docs

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.5.3 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@9.5.3...9.5.6)

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

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