Bump mkdocs from 1.0.4 to 1.2.3 in /docs

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.0.4 to 1.2.3.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.0.4...1.2.3)

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

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

docs/requirements_frozen.txt

@@ -5,7 +5,7 @@ jsmin==2.2.2
 livereload==2.6.1
 Markdown==3.1.1
 MarkupSafe==1.1.1
-mkdocs==1.0.4
+mkdocs==1.2.3
 mkdocs-material==4.6.0
 mkdocs-minify-plugin==0.2.1
 pep562==1.0