chore(deps): bump mkdocs from 1.1.2 to 1.2.3 in /docs

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.1.2 to 1.2.3.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.1.2...1.2.3)

---
updated-dependencies:
- dependency-name: mkdocs
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,5 +1,5 @@
 zillion
-mkdocs==1.1.2
+mkdocs==1.2.3
 mkdocs-material==5.2.1
 mkdocs-material-extensions==1.0
 mkdocs-minify-plugin==0.3.0