Bump mkdocs-material[imaging] from 9.5.14 to 9.5.15 in /docs

Bumps [mkdocs-material[imaging]](https://github.com/squidfunk/mkdocs-material) from 9.5.14 to 9.5.15.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.5.14...9.5.15)

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

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

docs/requirements.txt

@@ -1,4 +1,4 @@
-mkdocs-material==9.5.14
+mkdocs-material==9.5.15
 mkdocs-material[imaging]==9.5.14
 mkdocs-minify-plugin==0.8.0
 mkdocs-git-revision-date-localized-plugin==1.2.4