Bump mkdocs-material from 9.6.18 to 9.6.20 (#967)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.6.18 to 9.6.20.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.6.18...9.6.20)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-version: 9.6.20
  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>

Author: dependabot[bot]

requirements.txt

@@ -1,2 +1,2 @@
 mkdocs==1.6.1
-mkdocs-material==9.6.18
+mkdocs-material==9.6.20