Bump afritzler/mkdocs-material from 7.2.5 to 7.2.8 in /docs

Bumps afritzler/mkdocs-material from 7.2.5 to 7.2.8.

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

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

docs/Dockerfile

@@ -1,4 +1,4 @@
-FROM ghcr.io/afritzler/mkdocs-material:7.2.5
+FROM ghcr.io/afritzler/mkdocs-material:7.2.8
 
 LABEL project=onmetal_api_documentation