Build: Bump mkdocs-material from 9.1.19 to 9.1.21 in /python (#8188)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.1.19 to 9.1.21.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.1.19...9.1.21)

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

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

python/mkdocs/requirements.txt

@@ -23,6 +23,6 @@ mkdocstrings-python==1.2.1
 mkdocs-literate-nav==0.6.0
 mkdocs-autorefs==0.4.1
 mkdocs-gen-files==0.5.0
-mkdocs-material==9.1.19
+mkdocs-material==9.1.21
 mkdocs-material-extensions==1.1.1
 mkdocs-section-index==0.3.5