Bump mkdocs-material from 8.1.5 to 8.1.7 in /docs (#331)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 8.1.5 to 8.1.7.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@8.1.5...8.1.7)

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

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,4 +1,4 @@
 markdown-include==0.6.0
 mike==1.1.2
 mkdocs-exclude==1.0.2
-mkdocs-material==8.1.5
+mkdocs-material==8.1.7