Bump mkdocs from 1.5.3 to 1.6.0 in /docs

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.5.3 to 1.6.0.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.5.3...1.6.0)

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

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

docs/requirements.txt

@@ -10,7 +10,7 @@ MarkupSafe==2.1.5
 mdx-truly-sane-lists==1.3
 mergedeep==1.3.4
 mike==2.1.0
-mkdocs==1.5.3
+mkdocs==1.6.0
 mkdocs-exclude==1.0.2
 mkdocs-macros-plugin==1.0.5
 mkdocs-material==9.5.18